diff --git a/compiler/src/main/pascal/blaise.codegen.native.x86_64.pas b/compiler/src/main/pascal/blaise.codegen.native.x86_64.pas
index 4e23e90..202687f 100644
--- a/compiler/src/main/pascal/blaise.codegen.native.x86_64.pas
+++ b/compiler/src/main/pascal/blaise.codegen.native.x86_64.pas
@@ -157,6 +157,10 @@ type
     { Number of exc frame global slots to emit for the program main body.
       Zero when no try stmts appear in the top-level program statements. }
     FProgExcFrameCount: Integer;
+    { True when the program-main body uses jumbo sets: two scratch bitmap
+      buffers (_jset_scratch_0/1) are emitted as .bss globals (main has no
+      frame, so set-op result/literal buffers live in static storage). }
+    FProgHasJumboSet: Boolean;
     { Whole-program multi-unit guard: the system-class (TObject /
       TCustomAttribute) class-name strings, typeinfo, vtables and field-cleanup
       stubs are emitted by the FIRST class section that runs (the first unit
@@ -631,7 +635,9 @@ begin
     tyDouble:                                   Result := 8;
     tySingle:                                   Result := 4;
     tySet:
-      if TSetTypeDesc(AType).BitCount > 32 then
+      if TSetTypeDesc(AType).IsJumbo() then
+        Result := TSetTypeDesc(AType).RawSize()   { inline byte-array bitmap }
+      else if TSetTypeDesc(AType).BitCount > 32 then
         Result := 8
       else
         Result := 4;
@@ -646,6 +652,21 @@ begin
   Result := (AType <> nil) and (AType.Kind in [tyDouble, tySingle]);
 end;
 
+{ True for a JUMBO (>64-member) set: an inline byte-array bitmap aggregate
+  (like a record / static array), operated on via the _Set* RTL helpers and
+  passed/returned by pointer.  Sets of 64 members or fewer stay register-sized. }
+function IsJumboSet(AType: TTypeDesc): Boolean;
+begin
+  Result := (AType <> nil) and (AType.Kind = tySet) and
+            TSetTypeDesc(AType).IsJumbo();
+end;
+
+{ Bitmap byte count of a jumbo set (= ceil(BitCount/8), <= 32). }
+function JumboSetNBytes(AType: TTypeDesc): Integer;
+begin
+  Result := TSetTypeDesc(AType).RawByteSize();
+end;
+
 { SysV AMD64 XMM argument registers, in order. }
 const
   SysVXmmArgRegs: array[0..7] of string =
@@ -795,7 +816,8 @@ var
   HasData, HasTbss: Boolean;
   InitCD:   TConstDecl;
 begin
-  if (FDataGlobals.Count = 0) and (FProgExcFrameCount = 0) then
+  if (FDataGlobals.Count = 0) and (FProgExcFrameCount = 0) and
+     (not FProgHasJumboSet) then
   begin
     Self.EmitStrLitSection();
     Exit;
@@ -810,6 +832,7 @@ begin
       HasData := True;
   end;
   if FProgExcFrameCount > 0 then HasData := True;
+  if FProgHasJumboSet then HasData := True;
   { Two passes: first .data globals, then .tbss threadvars. }
   if HasData then
     Self.Emit('.data');
@@ -854,7 +877,8 @@ begin
       Continue;
     end;
     if (Self.GlobalType(Name) <> nil) and
-       (Self.GlobalType(Name).Kind in [tyRecord, tyStaticArray]) then
+       (IsJumboSet(Self.GlobalType(Name)) or
+          (Self.GlobalType(Name).Kind in [tyRecord, tyStaticArray])) then
     begin
       Sz := Self.GlobalType(Name).RawSize();
       Self.Emit('.balign 8');
@@ -904,6 +928,17 @@ begin
     Self.Emit('_exc_frame_' + IntToStr(I) + ':');
     Self.Emit(#9'.skip 512');
   end;
+  { Jumbo-set scratch buffers for the program-main body (32 bytes each, the
+    256-member maximum). }
+  if FProgHasJumboSet then
+  begin
+    Self.Emit('.balign 8');
+    Self.Emit('_jset_scratch_0:');
+    Self.Emit(#9'.skip 32');
+    Self.Emit('.balign 8');
+    Self.Emit('_jset_scratch_1:');
+    Self.Emit(#9'.skip 32');
+  end;
   { Threadvar globals: emit in .tbss (zero-initialised thread-local storage). }
   if HasTbss then
   begin
@@ -913,7 +948,8 @@ begin
       Name := FDataGlobals.Keys[I];
       if not Self.IsThreadVarGlobal(Name) then Continue;
       if (Self.GlobalType(Name) <> nil) and
-         (Self.GlobalType(Name).Kind in [tyRecord, tyStaticArray]) then
+         (IsJumboSet(Self.GlobalType(Name)) or
+          (Self.GlobalType(Name).Kind in [tyRecord, tyStaticArray])) then
         Sz := Self.GlobalType(Name).RawSize()
       else if (Self.GlobalType(Name) <> nil) and
               (Self.GlobalType(Name).Kind = tyDouble) then
@@ -1157,6 +1193,25 @@ begin
   for I := 0 to ABlock.ConstDecls.Count - 1 do
   begin
     CD := TConstDecl(ABlock.ConstDecls.Items[I]);
+    { Jumbo set constant: emit the bitmap as a byte blob under the mangled
+      label (shares the const-data pass with array consts). }
+    if (CD.ConstSetBytes <> nil) and (CD.ConstSetBytes.Count > 0) then
+    begin
+      if APrefix <> '' then
+        Lbl := APrefix + '_' + CD.Name
+      else if CD.ResolvedSetQbeName <> '' then
+        Lbl := NativeMangle(CD.ResolvedSetQbeName)
+      else
+        Lbl := CD.Name;
+      Self.Emit('.data');
+      Self.Emit('.balign 8');
+      if Copy(Lbl, 1, 2) <> '.L' then
+        Self.Emit('.globl ' + Lbl);
+      Self.Emit(Lbl + ':');
+      for J := 0 to CD.ConstSetBytes.Count - 1 do
+        Self.Emit(Format(#9'.byte %s', [CD.ConstSetBytes[J]]));
+      Continue;
+    end;
     if not CD.IsArrayConst then Continue;
     if (CD.ArrayElements = nil) or (CD.ArrayElements.Count = 0) then Continue;
     if APrefix <> '' then
@@ -3254,8 +3309,9 @@ procedure TX86_64Backend.AddSlot(const AName: string; AType: TTypeDesc;
 var
   Sz: Integer;
 begin
-  if (AType <> nil) and (AType.Kind in [tyRecord, tyStaticArray]) then
-    Sz := (AType.RawSize() + 7) and (-8)
+  if ((AType <> nil) and (AType.Kind in [tyRecord, tyStaticArray])) or
+     IsJumboSet(AType) then
+    Sz := (AType.RawSize() + 7) and (-8)   { full inline aggregate slot }
   else if (AType <> nil) and (AType.Kind = tyInterface) then
     Sz := 16   { fat pointer: obj slot (+0) then itab slot (+8) }
   else if (AType <> nil) and (AType.Kind = tyProcedural) and
@@ -3274,6 +3330,7 @@ var
   I, J, K, Offset, StackOff, TryCount, IntIdx2: Integer;
   P:    TMethodParam;
   VD:   TVarDecl;
+  HasJumbo: Boolean;
 begin
   Self.ClearFrame();
   FFrame      := TDictionary<string, Integer>.Create();
@@ -3352,7 +3409,8 @@ begin
         Inc(IntIdx2);
       end
       else if (P.ResolvedType <> nil) and
-              (P.ResolvedType.Kind in [tyRecord, tyStaticArray]) and
+              ((P.ResolvedType.Kind in [tyRecord, tyStaticArray]) or
+               IsJumboSet(P.ResolvedType)) and
               not P.IsVarParam then
       begin
         if IntIdx2 < 6 then
@@ -3395,8 +3453,11 @@ begin
     buffer and the epilogue loads it into rax/rdx/xmm0/xmm1. }
   if ADecl.ResolvedReturnType <> nil then
   begin
-    if ADecl.ResolvedReturnType.Kind = tyInterface then
+    if (ADecl.ResolvedReturnType.Kind = tyInterface) or
+       IsJumboSet(ADecl.ResolvedReturnType) then
     begin
+      { Interface and jumbo-set returns are sret: a hidden pointer arg; the
+        Result slot holds that pointer. }
       FSretFunc := True;
       Self.AddSlot('Result', nil, Offset);
     end
@@ -3455,6 +3516,26 @@ begin
     for K := 0 to TryCount - 1 do
       Self.AddSlot('_for_end_' + IntToStr(K), nil, Offset);
   end;
+  { Jumbo-set scratch slots: a jumbo set literal, union, intersection, or
+    difference produces a new bitmap that must live somewhere addressable.
+    Such a value can appear deep inside any expression (e.g. 'X in [members]'
+    over a >64-member enum, which is common in the compiler's own token tests),
+    so rather than walk the whole body we reserve the two 32-byte scratch slots
+    in every function frame.  The cost is 64 bytes per frame; correctness and
+    self-host stability outweigh it.  HasJumbo is retained for future
+    refinement to a body-walk-gated reservation. }
+  HasJumbo := True;
+  if HasJumbo then
+  begin
+    Inc(Offset, 32);
+    Offset := (Offset + 7) and (-8);
+    FFrame.Add('_jset_scratch_0', -Offset);
+    FFrameTypes.Add('_jset_scratch_0', nil);
+    Inc(Offset, 32);
+    Offset := (Offset + 7) and (-8);
+    FFrame.Add('_jset_scratch_1', -Offset);
+    FFrameTypes.Add('_jset_scratch_1', nil);
+  end;
   { Round the reserved size up to a 16-byte multiple (SysV alignment).
     -16 is the bitmask not(15) in two's complement (Blaise `not` is Boolean). }
   FFrameSize := (Offset + 15) and (-16);
@@ -4631,7 +4712,8 @@ begin
         Self.Emit(Format(#9'addq $%d, %%rcx',
           [TFieldInfo(TIdentExpr(AExpr).ImplicitFieldInfo).Offset]));
       if (TIdentExpr(AExpr).ResolvedType <> nil) and
-         (TIdentExpr(AExpr).ResolvedType.Kind in [tyRecord, tyStaticArray]) then
+         (IsJumboSet(TIdentExpr(AExpr).ResolvedType) or
+          (TIdentExpr(AExpr).ResolvedType.Kind in [tyRecord, tyStaticArray])) then
         Self.Emit(#9'movq %rcx, %rax')
       else if (TIdentExpr(AExpr).ResolvedType <> nil) and
               (TIdentExpr(AExpr).ResolvedType.Kind = tyClass) then
@@ -4641,7 +4723,8 @@ begin
       Exit;
     end;
     if (TIdentExpr(AExpr).ResolvedType <> nil) and
-       (TIdentExpr(AExpr).ResolvedType.Kind in [tyRecord, tyStaticArray]) then
+       (IsJumboSet(TIdentExpr(AExpr).ResolvedType) or
+          (TIdentExpr(AExpr).ResolvedType.Kind in [tyRecord, tyStaticArray])) then
     begin
       if FSretFunc and (TIdentExpr(AExpr).Name = 'Result') then
         Self.Emit(Format(#9'movq %s, %%rax', [Self.VarOperand('Result')]))
@@ -5733,8 +5816,20 @@ begin
        (BE.Right.ResolvedType <> nil) and
        (BE.Right.ResolvedType.Kind = tySet) then
     begin
+      if IsJumboSet(BE.Right.ResolvedType) then
+      begin
+        { Jumbo: evaluate ordinal, save it, get the set's bitmap address, then
+          _SetIn(rdi=set, esi=ord). }
+        Self.EmitExprToEax(BE.Left);
+        Self.Emit(#9'pushq %rax');           { ordinal }
+        Self.EmitExprToEax(BE.Right);        { set bitmap addr -> %rax }
+        Self.Emit(#9'movq %rax, %rdi');
+        Self.Emit(#9'popq %rsi');
+        Self.Emit(#9'callq _SetIn');
+        Exit;
+      end;
       Self.EmitExprToEax(BE.Left);
-      Self.Emit(#9'movl %eax, %ecx');
+      Self.Emit(#9'movl %eax, %ecx');       { ordinal in %ecx (and %cl) }
       Self.EmitExprToEax(BE.Right);
       if TSetTypeDesc(BE.Right.ResolvedType).BitCount > 32 then
       begin
@@ -5746,13 +5841,64 @@ begin
         Self.Emit(#9'shrl %cl, %eax');
         Self.Emit(#9'andl $1, %eax');
       end;
+      { Range guard: force 0 when the ordinal is >= the set width.  The set may
+        be sized to a literal's max ordinal (X in [low members]) while the
+        tested element's ordinal is larger; x86 shift counts wrap mod 32/64, so
+        the raw shift result for an out-of-range ordinal is meaningless and
+        must be masked out.  %edx = (ord < BitCount) ? 1 : 0. }
+      Self.Emit(Format(#9'cmpl $%d, %%ecx',
+        [TSetTypeDesc(BE.Right.ResolvedType).BitCount]));
+      Self.Emit(#9'setl %dl');
+      Self.Emit(#9'movzbl %dl, %edx');
+      Self.Emit(#9'andl %edx, %eax');
       Exit;
     end;
-    { Set arithmetic: union (+), difference (-), intersection (*) }
+    { Set arithmetic: union (+), difference (-), intersection (*), equality. }
     if (BE.Left.ResolvedType <> nil) and
        (BE.Left.ResolvedType.Kind = tySet) and
        (BE.Op in [boAdd, boSub, boMul, boEQ, boNE]) then
     begin
+      if IsJumboSet(BE.Left.ResolvedType) then
+      begin
+        { Equality compares two bitmap addresses via _SetEqual. }
+        if BE.Op in [boEQ, boNE] then
+        begin
+          Self.EmitExprToEax(BE.Left);
+          Self.Emit(#9'pushq %rax');
+          Self.EmitExprToEax(BE.Right);
+          Self.Emit(#9'movq %rax, %rsi');
+          Self.Emit(#9'popq %rdi');
+          Self.Emit(Format(#9'movl $%d, %%edx',
+            [JumboSetNBytes(BE.Left.ResolvedType)]));
+          Self.Emit(#9'callq _SetEqual');
+          if BE.Op = boNE then
+            Self.Emit(#9'xorl $1, %eax');
+          Exit;
+        end;
+        { Union/intersection/difference: write the result into a frame scratch
+          slot and return its address.  The _Set helper takes rdi=dest,
+          rsi=A, rdx=B, ecx=nbytes. %r12/%r13 are callee-saved across the two
+          operand evaluations and the helper call. }
+        Self.EmitExprToEax(BE.Left);
+        Self.Emit(#9'pushq %r12');
+        Self.Emit(#9'pushq %r13');
+        Self.Emit(#9'movq %rax, %r12');         { A addr }
+        Self.EmitExprToEax(BE.Right);
+        Self.Emit(#9'movq %rax, %r13');         { B addr }
+        Self.Emit(Format(#9'leaq %s, %%rdi', [Self.VarOperand('_jset_scratch_0')]));
+        Self.Emit(#9'movq %r12, %rsi');
+        Self.Emit(#9'movq %r13, %rdx');
+        Self.Emit(Format(#9'movl $%d, %%ecx', [JumboSetNBytes(BE.Left.ResolvedType)]));
+        case BE.Op of
+          boAdd: Self.Emit(#9'callq _SetUnion');
+          boMul: Self.Emit(#9'callq _SetInter');
+          boSub: Self.Emit(#9'callq _SetDiff');
+        end;
+        Self.Emit(Format(#9'leaq %s, %%rax', [Self.VarOperand('_jset_scratch_0')]));
+        Self.Emit(#9'popq %r13');
+        Self.Emit(#9'popq %r12');
+        Exit;
+      end;
       Self.EmitExprToEax(BE.Left);
       Self.Emit(#9'pushq %rax');
       Self.EmitExprToEax(BE.Right);
@@ -6215,7 +6361,8 @@ begin
     Self.Emit(#9'movq %rax, %rcx');
     if FAE.FieldInfo.Offset > 0 then
       Self.Emit(Format(#9'leaq %d(%%rcx), %%rcx', [FAE.FieldInfo.Offset]));
-    if FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray] then
+    if (IsJumboSet(FAE.FieldInfo.TypeDesc) or
+         (FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray])) then
       Self.Emit(#9'movq %rcx, %rax')
     else
       Self.EmitLoadVar('(%rcx)', FAE.FieldInfo.TypeDesc);
@@ -6238,7 +6385,8 @@ begin
         Self.Emit(Format(#9'addq $%d, %%rcx', [FAE.ImplicitBaseInfo.Offset]));
       if FAE.IsClassAccess then
         Self.Emit(#9'movq (%rcx), %rcx');
-      if FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray] then
+      if (IsJumboSet(FAE.FieldInfo.TypeDesc) or
+         (FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray])) then
         Self.Emit(Format(#9'leaq %d(%%rcx), %%rax', [FAE.FieldInfo.Offset]))
       else
         Self.EmitLoadVar(Format('%d(%%rcx)', [FAE.FieldInfo.Offset]),
@@ -6253,7 +6401,8 @@ begin
       if FAE.IsVarParam then
         { var-param class: slot -> caller var -> instance }
         Self.Emit(#9'movq (%rcx), %rcx');
-      if FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray] then
+      if (IsJumboSet(FAE.FieldInfo.TypeDesc) or
+         (FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray])) then
         Self.Emit(Format(#9'leaq %d(%%rcx), %%rax', [FAE.FieldInfo.Offset]))
       else
         Self.EmitLoadVar(Format('%d(%%rcx)', [FAE.FieldInfo.Offset]),
@@ -6265,7 +6414,8 @@ begin
         Self.Emit(Format(#9'movq %s, %%rcx', [Self.VarOperand(FAE.RecordName)]))
       else
         Self.Emit(Format(#9'movq %s(%%rip), %%rcx', [FAE.RecordName]));
-      if FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray] then
+      if (IsJumboSet(FAE.FieldInfo.TypeDesc) or
+         (FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray])) then
         Self.Emit(Format(#9'leaq %d(%%rcx), %%rax', [FAE.FieldInfo.Offset]))
       else
         Self.EmitLoadVar(Format('%d(%%rcx)', [FAE.FieldInfo.Offset]),
@@ -6273,7 +6423,8 @@ begin
     end
     else if Self.IsLocal(FAE.RecordName) then
     begin
-      if FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray] then
+      if (IsJumboSet(FAE.FieldInfo.TypeDesc) or
+         (FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray])) then
       begin
         Self.Emit(Format(#9'leaq %s, %%rcx', [Self.VarOperand(FAE.RecordName)]));
         if FAE.FieldInfo.Offset = 0 then
@@ -6292,7 +6443,8 @@ begin
     end
     else
     begin
-      if FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray] then
+      if (IsJumboSet(FAE.FieldInfo.TypeDesc) or
+         (FAE.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray])) then
       begin
         Self.Emit(Format(#9'leaq %s(%%rip), %%rcx', [FAE.RecordName]));
         if FAE.FieldInfo.Offset = 0 then
@@ -6605,6 +6757,27 @@ begin
   if (AExpr is TArrayLiteralExpr) and
      (AExpr.ResolvedType <> nil) and (AExpr.ResolvedType.Kind = tySet) then
   begin
+    { Jumbo set literal: build the bitmap in the scratch_1 slot — memset 0,
+      then _SetInclude per element (elements may be non-constant).  Return the
+      buffer address.  scratch_1 (not scratch_0) so a surrounding set-op
+      assignment, which uses scratch_0, is not clobbered. }
+    if IsJumboSet(AExpr.ResolvedType) then
+    begin
+      Self.Emit(Format(#9'leaq %s, %%rdi', [Self.VarOperand('_jset_scratch_1')]));
+      Self.Emit(#9'xorl %esi, %esi');
+      Self.Emit(Format(#9'movl $%d, %%edx', [TSetTypeDesc(AExpr.ResolvedType).RawSize()]));
+      Self.Emit(#9'callq memset');
+      for SetI := 0 to TArrayLiteralExpr(AExpr).Elements.Count - 1 do
+      begin
+        SetElem := TASTExpr(TArrayLiteralExpr(AExpr).Elements.Items[SetI]);
+        Self.EmitExprToEax(SetElem);
+        Self.Emit(#9'movl %eax, %esi');     { ordinal }
+        Self.Emit(Format(#9'leaq %s, %%rdi', [Self.VarOperand('_jset_scratch_1')]));
+        Self.Emit(#9'callq _SetInclude');
+      end;
+      Self.Emit(Format(#9'leaq %s, %%rax', [Self.VarOperand('_jset_scratch_1')]));
+      Exit;
+    end;
     SetMask := 0;
     for SetI := 0 to TArrayLiteralExpr(AExpr).Elements.Count - 1 do
     begin
@@ -6623,7 +6796,8 @@ begin
   begin
     Self.EmitExprToEax(TDerefExpr(AExpr).Expr);
     if (AExpr.ResolvedType <> nil) and
-       (AExpr.ResolvedType.Kind in [tyRecord, tyStaticArray]) then
+       (IsJumboSet(AExpr.ResolvedType) or
+       (AExpr.ResolvedType.Kind in [tyRecord, tyStaticArray])) then
     begin
       { Pointer-to-record/array: the pointer value IS the record address.
         Callers (field access, assignment) work with addresses for records. }
@@ -8123,8 +8297,16 @@ begin
     Self.Emit(#9'jmp ' + LEnd);
 
     Self.Emit(LBody + ':');
-    { Test bit: (mask >> idx) & 1 }
-    if AStmt.SetBitCount > 32 then
+    { Test bit: jumbo via _SetIn(set_addr, idx); else (mask >> idx) & 1 }
+    if AStmt.SetIsJumbo then
+    begin
+      Self.Emit(Format(#9'movq %s, %%rdi',
+        [Self.VarOperand(AStmt.SetMaskVarName)]));   { set bitmap addr }
+      Self.Emit(Format(#9'movl %s, %%esi', [IdxOp]));
+      Self.Emit(#9'callq _SetIn');
+      Self.Emit(#9'testl %eax, %eax');
+    end
+    else if AStmt.SetBitCount > 32 then
     begin
       Self.Emit(Format(#9'movq %s, %%rax',
         [Self.VarOperand(AStmt.SetMaskVarName)]));
@@ -8843,6 +9025,21 @@ begin
           '(%rbx)', False);
         Self.Emit(#9'popq %rbx');
       end
+      else if IsJumboSet(Asgn.ResolvedLhsType) then
+      begin
+        { Jumbo set into an implicit-Self field: plain bitmap memcpy (a set has
+          no managed fields, so no retain/release). }
+        Self.EmitExprToEax(Asgn.Expr);
+        Self.Emit(#9'pushq %rbx');
+        Self.Emit(#9'movq %rax, %rbx');         { source bitmap addr }
+        Self.Emit(Format(#9'movq %s, %%rdi', [Self.VarOperand('Self')]));
+        if ISFld.Offset > 0 then
+          Self.Emit(Format(#9'addq $%d, %%rdi', [ISFld.Offset]));
+        Self.Emit(#9'movq %rbx, %rsi');
+        Self.Emit(Format(#9'movq $%d, %%rdx', [Asgn.ResolvedLhsType.RawSize()]));
+        Self.Emit(#9'callq memcpy');
+        Self.Emit(#9'popq %rbx');
+      end
       else if (Asgn.ResolvedLhsType.Kind in [tyRecord, tyStaticArray]) then
       begin
         Self.EmitExprToEax(Asgn.Expr);
@@ -8955,15 +9152,19 @@ begin
       Self.Emit(#9'callq memcpy');
       Exit;
     end;
-    { sret assignment: LHS is a record variable; RHS is a record-returning call.
-      Pass the destination buffer address as the hidden first arg (%rdi). }
+    { sret assignment: LHS is a record (or jumbo set) variable; RHS is a
+      record/jumbo-set-returning call.  Pass the destination buffer address as
+      the hidden first arg (%rdi). }
     if (Asgn.ResolvedLhsType <> nil) and
-       (Asgn.ResolvedLhsType.Kind = tyRecord) and
+       ((Asgn.ResolvedLhsType.Kind = tyRecord) or IsJumboSet(Asgn.ResolvedLhsType)) and
        (Asgn.Expr is TFuncCallExpr) and
        (TFuncCallExpr(Asgn.Expr).ResolvedDecl <> nil) and
        (TMethodDecl(TFuncCallExpr(Asgn.Expr).ResolvedDecl).ResolvedReturnType <> nil) and
-       (TMethodDecl(TFuncCallExpr(Asgn.Expr).ResolvedDecl).ResolvedReturnType.Kind = tyRecord) then
+       ((TMethodDecl(TFuncCallExpr(Asgn.Expr).ResolvedDecl).ResolvedReturnType.Kind = tyRecord) or
+        IsJumboSet(TMethodDecl(TFuncCallExpr(Asgn.Expr).ResolvedDecl).ResolvedReturnType)) then
     begin
+      { For a local jumbo set the dest is leaq'd; EmitSretCall's caller passes
+        the operand and a 'by-ref' flag.  Mirror the record dispatch below. }
       if FSretFunc and SameText(Asgn.Name, 'Result') then
         Self.EmitSretCall(
           FuncSymbolOf(TFuncCallExpr(Asgn.Expr)),
@@ -8983,21 +9184,25 @@ begin
           TFuncCallExpr(Asgn.Expr).Args,
           Self.VarOperand(Asgn.Name), False)
       else
+      begin
+        Self.AddGlobal(Asgn.Name, Asgn.ResolvedLhsType);
         Self.EmitSretCall(
           FuncSymbolOf(TFuncCallExpr(Asgn.Expr)),
           TMethodDecl(TFuncCallExpr(Asgn.Expr).ResolvedDecl),
           TFuncCallExpr(Asgn.Expr).Args,
           Asgn.Name + '(%rip)', False);
+      end;
       Exit;
     end;
-    { sret assignment: method call returning a record.
+    { sret assignment: method call returning a record (or jumbo set).
       %rdi = sret ptr, %rsi = Self, %rdx.. = user args. }
     if (Asgn.ResolvedLhsType <> nil) and
-       (Asgn.ResolvedLhsType.Kind = tyRecord) and
+       ((Asgn.ResolvedLhsType.Kind = tyRecord) or IsJumboSet(Asgn.ResolvedLhsType)) and
        (Asgn.Expr is TMethodCallExpr) and
        (TMethodCallExpr(Asgn.Expr).ResolvedMethod <> nil) and
        (TMethodDecl(TMethodCallExpr(Asgn.Expr).ResolvedMethod).ResolvedReturnType <> nil) and
-       (TMethodDecl(TMethodCallExpr(Asgn.Expr).ResolvedMethod).ResolvedReturnType.Kind = tyRecord) then
+       ((TMethodDecl(TMethodCallExpr(Asgn.Expr).ResolvedMethod).ResolvedReturnType.Kind = tyRecord) or
+        IsJumboSet(TMethodDecl(TMethodCallExpr(Asgn.Expr).ResolvedMethod).ResolvedReturnType)) then
     begin
       if FSretFunc and SameText(Asgn.Name, 'Result') then
         Self.EmitMethodSretCall(TMethodCallExpr(Asgn.Expr),
@@ -9009,8 +9214,11 @@ begin
         Self.EmitMethodSretCall(TMethodCallExpr(Asgn.Expr),
           Self.VarOperand(Asgn.Name), False)
       else
+      begin
+        Self.AddGlobal(Asgn.Name, Asgn.ResolvedLhsType);
         Self.EmitMethodSretCall(TMethodCallExpr(Asgn.Expr),
           Asgn.Name + '(%rip)', False);
+      end;
       Exit;
     end;
     if IsFloatFamily(Asgn.ResolvedLhsType) then
@@ -9206,7 +9414,8 @@ begin
       end;
     end
     else if (Asgn.ResolvedLhsType <> nil) and
-            (Asgn.ResolvedLhsType.Kind in [tyRecord, tyStaticArray]) then
+            (IsJumboSet(Asgn.ResolvedLhsType) or
+             (Asgn.ResolvedLhsType.Kind in [tyRecord, tyStaticArray])) then
     begin
       Self.EmitExprToEax(Asgn.Expr);
       Self.Emit(#9'movq %rax, %rsi');
@@ -9444,6 +9653,18 @@ begin
     { Include(S, elem): S := S or (1 shl ord(elem)) }
     if SameText(PC.Name, 'Include') and (PC.Args.Count = 2) then
     begin
+      { Jumbo set: address of the set, ordinal, then _SetInclude. Handles any
+        lvalue shape (var, field, element), not just a bare ident. }
+      if IsJumboSet(TASTExpr(PC.Args.Items[0]).ResolvedType) then
+      begin
+        Self.EmitExprToEax(TASTExpr(PC.Args.Items[1]));
+        Self.Emit(#9'pushq %rax');           { ordinal }
+        Self.EmitExprToEax(TASTExpr(PC.Args.Items[0]));  { set addr -> %rax }
+        Self.Emit(#9'movq %rax, %rdi');
+        Self.Emit(#9'popq %rsi');
+        Self.Emit(#9'callq _SetInclude');
+        Exit;
+      end;
       Self.EmitExprToEax(TASTExpr(PC.Args.Items[1]));
       Self.Emit(#9'movl %eax, %ecx');
       FDynArgName := TIdentExpr(TASTExpr(PC.Args.Items[0])).Name;
@@ -9473,6 +9694,17 @@ begin
     { Exclude(S, elem): S := S and (not (1 shl ord(elem))) }
     if SameText(PC.Name, 'Exclude') and (PC.Args.Count = 2) then
     begin
+      { Jumbo set: address of the set, ordinal, then _SetExclude. }
+      if IsJumboSet(TASTExpr(PC.Args.Items[0]).ResolvedType) then
+      begin
+        Self.EmitExprToEax(TASTExpr(PC.Args.Items[1]));
+        Self.Emit(#9'pushq %rax');
+        Self.EmitExprToEax(TASTExpr(PC.Args.Items[0]));
+        Self.Emit(#9'movq %rax, %rdi');
+        Self.Emit(#9'popq %rsi');
+        Self.Emit(#9'callq _SetExclude');
+        Exit;
+      end;
       Self.EmitExprToEax(TASTExpr(PC.Args.Items[1]));
       Self.Emit(#9'movl %eax, %ecx');
       FDynArgName := TIdentExpr(TASTExpr(PC.Args.Items[0])).Name;
@@ -12194,13 +12426,14 @@ begin
     Self.Emit(Format(#9'leaq %s, %%rax', [ASretAddr]));
   Self.Emit(#9'pushq %rax');
   { Zero the destination buffer via memset(dest, 0, size), mirroring the QBE
-    backend.  ADecl.ResolvedReturnType.Kind = tyRecord here. }
+    backend.  The return type is a record or a jumbo set here; RawSize covers
+    both (TotalSize for a record, the bitmap byte count for a jumbo set). }
   if (ADecl <> nil) and (ADecl.ResolvedReturnType <> nil) then
   begin
     Self.Emit(#9'movq (%rsp), %rdi');
     Self.Emit(#9'xorl %esi, %esi');
     Self.Emit(Format(#9'movq $%d, %%rdx',
-      [TRecordTypeDesc(ADecl.ResolvedReturnType).TotalSize()]));
+      [ADecl.ResolvedReturnType.RawSize()]));
     Self.Emit(#9'callq memset');
   end;
   HD := TList<Integer>.Create();
@@ -12377,7 +12610,7 @@ begin
     Self.Emit(#9'movq (%rsp), %rdi');
     Self.Emit(#9'xorl %esi, %esi');
     Self.Emit(Format(#9'movq $%d, %%rdx',
-      [TRecordTypeDesc(MD.ResolvedReturnType).TotalSize()]));
+      [MD.ResolvedReturnType.RawSize()]));
     Self.Emit(#9'callq memset');
   end;
 
@@ -13220,7 +13453,8 @@ begin
       end;
     end
     else if (P.ResolvedType <> nil) and
-            (P.ResolvedType.Kind in [tyRecord, tyStaticArray]) then
+            ((P.ResolvedType.Kind in [tyRecord, tyStaticArray]) or
+             IsJumboSet(P.ResolvedType)) then
     begin
       { Phase 1: spill only the incoming pointer.  The local copy is made
         AFTER every register is spilled — memcpy clobbers the caller-saved
@@ -13250,7 +13484,8 @@ begin
     P := TMethodParam(ADecl.Params.Items[I]);
     if P.IsOpenArray or P.IsVarParam then Continue;
     if (P.ResolvedType = nil) or
-       not (P.ResolvedType.Kind in [tyRecord, tyStaticArray]) then Continue;
+       not ((P.ResolvedType.Kind in [tyRecord, tyStaticArray]) or
+            IsJumboSet(P.ResolvedType)) then Continue;
     Self.Emit(Format(#9'movq %s, %%rsi', [Self.VarOperand(P.ParamName)]));
     Self.Emit(Format(#9'leaq %s, %%rdi',
       [Self.VarOperand(P.ParamName + '_data')]));
@@ -13332,7 +13567,17 @@ begin
 
         tySet:
           for J := 0 to TVarDecl(ADecl.Body.Decls.Items[I]).Names.Count - 1 do
-            if TSetTypeDesc(TVarDecl(ADecl.Body.Decls.Items[I]).ResolvedType).BitCount <= 32 then
+            if IsJumboSet(TVarDecl(ADecl.Body.Decls.Items[I]).ResolvedType) then
+            begin
+              { Jumbo set: zero the whole inline bitmap via memset. }
+              Self.Emit(Format(#9'leaq %s, %%rdi',
+                [Self.VarOperand(TVarDecl(ADecl.Body.Decls.Items[I]).Names.Strings[J])]));
+              Self.Emit(#9'xorl %esi, %esi');
+              Self.Emit(Format(#9'movl $%d, %%edx',
+                [TSetTypeDesc(TVarDecl(ADecl.Body.Decls.Items[I]).ResolvedType).RawSize()]));
+              Self.Emit(#9'callq memset');
+            end
+            else if TSetTypeDesc(TVarDecl(ADecl.Body.Decls.Items[I]).ResolvedType).BitCount <= 32 then
               Self.Emit(Format(#9'movl $0, %s',
                 [Self.VarOperand(TVarDecl(ADecl.Body.Decls.Items[I]).Names.Strings[J])]))
             else
@@ -13640,6 +13885,11 @@ begin
   for I := 0 to AProg.Block.Stmts.Count - 1 do
     FProgExcFrameCount := FProgExcFrameCount +
       Self.CountTryStmts(TASTStmt(AProg.Block.Stmts.Items[I]));
+  { Jumbo-set scratch in main: main has no stack frame, so set literal / set-op
+    result buffers live in static .bss.  A jumbo set value can appear in any
+    expression in the program body (e.g. 'X in [members]' over a >64 enum), so
+    always reserve the two scratch buffers. }
+  FProgHasJumboSet := True;
   { Reset per-function state before emitting the program body. }
   FExcDepth     := 0;
   FExcFrameNext := 0;
diff --git a/compiler/src/main/pascal/blaise.codegen.qbe.pas b/compiler/src/main/pascal/blaise.codegen.qbe.pas
index 383c839..ef36b1d 100644
--- a/compiler/src/main/pascal/blaise.codegen.qbe.pas
+++ b/compiler/src/main/pascal/blaise.codegen.qbe.pas
@@ -197,6 +197,11 @@ type
     procedure EmitFuncDef(ADecl: TMethodDecl; AExported: Boolean);
     procedure EmitBlock(ABlock: TBlock);
     procedure EmitVarAllocs(ABlock: TBlock);
+    { True for inline-aggregate value types whose "value" in QBE is the
+      ADDRESS of their storage (not a loaded register): records, static arrays,
+      and JUMBO (>64-member) sets.  Used at the read/arg/return sites that must
+      return a storage address rather than a loaded scalar. }
+    function  IsAggregateAddrType(AType: TTypeDesc): Boolean;
     { mem2reg helpers }
     { Returns True if AKind is a scalar type promotable to a QBE SSA temp. }
     function  IsPromotableKind(AKind: TTypeKind): Boolean;
@@ -1007,6 +1012,11 @@ function TCodeGenQBE.QbeParamTypeOf(AType: TTypeDesc): string;
 begin
   if (AType <> nil) and (AType.Kind = tyRecord) then
     Result := FFIRecordTypeRef(TRecordTypeDesc(AType))
+  { Jumbo set: passed by pointer to its bitmap (the callee copies it into a
+    local slot for value semantics). }
+  else if (AType <> nil) and (AType.Kind = tySet) and
+          TSetTypeDesc(AType).IsJumbo() then
+    Result := 'l'
   else
     Result := QbeTypeOf(AType);
 end;
@@ -1194,6 +1204,13 @@ end;
   mem2reg helpers
   ----------------------------------------------------------------------- }
 
+function TCodeGenQBE.IsAggregateAddrType(AType: TTypeDesc): Boolean;
+begin
+  if AType = nil then Exit(False);
+  Result := (AType.Kind in [tyRecord, tyStaticArray]) or
+            ((AType.Kind = tySet) and TSetTypeDesc(AType).IsJumbo());
+end;
+
 function TCodeGenQBE.IsPromotableKind(AKind: TTypeKind): Boolean;
 begin
   { Only promote pure scalar types that are never used as receivers for
@@ -1619,6 +1636,12 @@ begin
             { tyProcedural method-pointers are two-slot aggregates — not promotable }
             IsMethodPtr := (Decl.ResolvedType.Kind = tyProcedural) and
                            TProceduralTypeDesc(Decl.ResolvedType).IsMethodPtr;
+            { Jumbo (>64-member) sets are inline byte-array aggregates, not
+              register values — promoting one to a single SSA temp would
+              silently truncate it to 8 bytes. }
+            if (Decl.ResolvedType.Kind = tySet) and
+               TSetTypeDesc(Decl.ResolvedType).IsJumbo() then
+              IsMethodPtr := True;
             if not IsMethodPtr then
             begin
               FPromotedLocals.Add(VarName);
@@ -1741,10 +1764,19 @@ begin
               EmitLine(Format('  %%_var_%s =l alloc4 1', [VarName]));
               EmitLine(Format('  storew 0, %%_var_%s', [VarName]));
             end
-            else
+            else if TSetTypeDesc(Decl.ResolvedType).BitCount <= 64 then
             begin
               EmitLine(Format('  %%_var_%s =l alloc8 1', [VarName]));
               EmitLine(Format('  storel 0, %%_var_%s', [VarName]));
+            end
+            else
+            begin
+              { Jumbo set: inline byte-array bitmap, zero-init via memset (like
+                a static array). }
+              ArrSize := TSetTypeDesc(Decl.ResolvedType).RawSize();
+              EmitLine(Format('  %%_var_%s =l alloc8 %d', [VarName, ArrSize]));
+              EmitLine(Format('  call $memset(l %%_var_%s, w 0, l %d)',
+                [VarName, ArrSize]));
             end;
           end;
 
@@ -1844,8 +1876,12 @@ begin
         tySet:
           if TSetTypeDesc(Decl.ResolvedType).BitCount <= 32 then
             EmitLine(Format('%s $%s = { w 0 }', [Pfx, VarName]))
+          else if TSetTypeDesc(Decl.ResolvedType).BitCount <= 64 then
+            EmitLine(Format('%s $%s = { l 0 }', [Pfx, VarName]))
           else
-            EmitLine(Format('%s $%s = { l 0 }', [Pfx, VarName]));
+            { Jumbo set: zero-filled inline byte-array bitmap. }
+            EmitLine(Format('%s $%s = { z %d }',
+              [Pfx, VarName, TSetTypeDesc(Decl.ResolvedType).RawSize()]));
         tyInt64, tyUInt64:
           EmitLine(Format('%s $%s = { l 0 }', [Pfx, VarName]));
         tyString, tyClass, tyPointer, tyPChar, tyMetaClass:
@@ -1983,6 +2019,28 @@ var
   IsStrArray: Boolean;
   Label_:     string;
 begin
+  { Jumbo set constant: emit the bitmap as a byte blob under the mangled label.
+    Shares the const-data pass with array consts. }
+  if (CD.ConstSetBytes <> nil) and (CD.ConstSetBytes.Count > 0) then
+  begin
+    if APrefix <> '' then
+      Label_ := APrefix + '_' + CD.Name
+    else if CD.ResolvedSetQbeName <> '' then
+      Label_ := CD.ResolvedSetQbeName
+    else
+      Label_ := CD.Name;
+    Parts := '';
+    for J := 0 to CD.ConstSetBytes.Count - 1 do
+    begin
+      if J > 0 then Parts := Parts + ', ';
+      Parts := Parts + Format('b %s', [CD.ConstSetBytes[J]]);
+    end;
+    if APrefix <> '' then
+      EmitLine(Format('export data $%s = { %s }', [Label_, Parts]))
+    else
+      EmitLine(Format('data $%s = { %s }', [Label_, Parts]));
+    Exit;
+  end;
   if not CD.IsArrayConst then Exit;
   if (CD.ArrayElements = nil) or (CD.ArrayElements.Count = 0) then Exit;
   if APrefix <> '' then
@@ -3263,9 +3321,15 @@ begin
       EmitLine(Format('  %s =w copy %s', [IdxW, IdxSlot]))
     else
       EmitLine(Format('  %s =w loadw %s', [IdxW, IdxSlot]));
-    EmitLine(Format('  %s =%s shr %s, %s', [BitT, SetMQT, MaskT, IdxW]));
     CmpT := AllocTemp();
-    EmitLine(Format('  %s =w and %s, 1', [CmpT, BitT]));
+    if AStmt.SetIsJumbo then
+      { Jumbo: MaskT is the set's bitmap address; test membership via _SetIn. }
+      EmitLine(Format('  %s =w call $_SetIn(l %s, w %s)', [CmpT, MaskT, IdxW]))
+    else
+    begin
+      EmitLine(Format('  %s =%s shr %s, %s', [BitT, SetMQT, MaskT, IdxW]));
+      EmitLine(Format('  %s =w and %s, 1', [CmpT, BitT]));
+    end;
     { If bit is 0 skip body, go directly to forin_next }
     EmitLine(Format('  jnz %s, @%s_yes, @%s', [CmpT, LblBody, LblNext]));
     EmitLine('@' + LblBody + '_yes');
@@ -4118,6 +4182,18 @@ begin
       EmitLine(Format('  %s %s, %s', [StoreInstr, ValTemp, PtrTemp]));
     end;
   end
+  else if (AAssign.ResolvedLhsType <> nil) and
+          (AAssign.ResolvedLhsType.Kind = tySet) and
+          TSetTypeDesc(AAssign.ResolvedLhsType).IsJumbo() then
+  begin
+    { Jumbo set assignment: the RHS evaluates to the source bitmap address
+      (a set variable, a set-op result buffer, or a const blob); copy the
+      whole bitmap into the destination slot. }
+    ValTemp := EmitExpr(AAssign.Expr);
+    EmitLine(Format('  call $memcpy(l %s, l %s, l %d)',
+      [VarRef(AAssign.Name, AAssign.IsGlobal), ValTemp,
+       TSetTypeDesc(AAssign.ResolvedLhsType).RawSize()]));
+  end
   else if (AAssign.ResolvedLhsType <> nil) and
           (AAssign.ResolvedLhsType.Kind = tyRecord) then
   begin
@@ -5160,6 +5236,18 @@ var
   ArgLine, RetT, AggRef: string;
   Sz: Integer;
 begin
+  { Jumbo set returns always use the plain sret path (a hidden dest pointer +
+    void return); they share this call helper with records but must not go
+    through ClassifyRecordReturn (which reads record-specific size fields). }
+  if (ARetType <> nil) and (TTypeDesc(ARetType).Kind = tySet) then
+  begin
+    if AVisibleArgs <> '' then
+      ArgLine := Format('l %s, %s', [ADestAddr, AVisibleArgs])
+    else
+      ArgLine := Format('l %s', [ADestAddr]);
+    EmitLine(Format('  call %s(%s)', [AFuncName, ArgLine]));
+    Exit;
+  end;
   case Self.ClassifyRecordReturn(ARetType) of
     rcSret:
       begin
@@ -6673,8 +6761,18 @@ begin
             [Par.ParamName, Par.ParamName]));
         end;
       tySet:
-        { A set is a w (≤32 members) or l (≤64) bitmask — spill at its width. }
-        if TSetTypeDesc(Par.ResolvedType).BitCount <= 32 then
+        { A small set is a w (<=32) / l (<=64) bitmask spilled at its width.
+          A jumbo set arrives as a pointer to the caller's bitmap; copy it into
+          a fresh local bitmap slot for value semantics. }
+        if TSetTypeDesc(Par.ResolvedType).IsJumbo() then
+        begin
+          EmitLine(Format('  %%_var_%s =l alloc8 %d',
+            [Par.ParamName, TSetTypeDesc(Par.ResolvedType).RawSize()]));
+          EmitLine(Format('  call $memcpy(l %%_var_%s, l %%_par_%s, l %d)',
+            [Par.ParamName, Par.ParamName,
+             TSetTypeDesc(Par.ResolvedType).RawSize()]));
+        end
+        else if TSetTypeDesc(Par.ResolvedType).BitCount <= 32 then
         begin
           EmitLine(Format('  %%_var_%s =l alloc4 1', [Par.ParamName]));
           EmitLine(Format('  storew %%_par_%s, %%_var_%s',
@@ -6748,7 +6846,9 @@ begin
     RC := Self.ClassifyRecordReturn(TRecordTypeDesc(AMethod.ResolvedReturnType));
 
   Sig := 'l %_par_Self';
-  if IsFunc and (AMethod.ResolvedReturnType.Kind = tyInterface) then
+  if IsFunc and ((AMethod.ResolvedReturnType.Kind = tyInterface) or
+     ((AMethod.ResolvedReturnType.Kind = tySet) and
+      TSetTypeDesc(AMethod.ResolvedReturnType).IsJumbo())) then
     Sig := 'l %_par__sret, l %_par_Self'
   else if IsFunc and (AMethod.ResolvedReturnType.Kind = tyRecord) then
     EmitRecordReturnSignature(Sig, RC);
@@ -6776,7 +6876,10 @@ begin
   if IsFunc then
   begin
     RetQType := QbeTypeOf(AMethod.ResolvedReturnType);
-    if AMethod.ResolvedReturnType.Kind = tyInterface then
+    if (AMethod.ResolvedReturnType.Kind = tyInterface) or
+       ((AMethod.ResolvedReturnType.Kind = tySet) and
+        TSetTypeDesc(AMethod.ResolvedReturnType).IsJumbo()) then
+      { sret aggregate return — void function. }
       EmitLine(Format('%sfunction %s(%s) {', [ExportPrefix(), FuncName, Sig]))
     else if AMethod.ResolvedReturnType.Kind = tyRecord then
     begin
@@ -6843,6 +6946,14 @@ begin
   begin
     if AMethod.ResolvedReturnType.Kind = tyRecord then
       EmitRecordReturnPrologue(TRecordTypeDesc(AMethod.ResolvedReturnType), RC)
+    else if (AMethod.ResolvedReturnType.Kind = tySet) and
+            TSetTypeDesc(AMethod.ResolvedReturnType).IsJumbo() then
+    begin
+      { sret: jumbo-set Result aliases the caller's buffer; zero-init it. }
+      EmitLine('  %_var_Result =l copy %_par__sret');
+      EmitLine(Format('  call $memset(l %%_var_Result, w 0, l %d)',
+        [TSetTypeDesc(AMethod.ResolvedReturnType).RawSize()]));
+    end
     else if AMethod.ResolvedReturnType.Kind = tyInterface then
     begin
       { sret: interface Result is a 16-byte fat pointer (obj+itab) in the
@@ -6919,7 +7030,10 @@ begin
   begin
     if AMethod.ResolvedReturnType.Kind = tyRecord then
       EmitRecordReturnEpilogue(TRecordTypeDesc(AMethod.ResolvedReturnType), RC)
-    else if AMethod.ResolvedReturnType.Kind = tyInterface then
+    else if (AMethod.ResolvedReturnType.Kind = tyInterface) or
+            ((AMethod.ResolvedReturnType.Kind = tySet) and
+             TSetTypeDesc(AMethod.ResolvedReturnType).IsJumbo()) then
+      { sret aggregate return — written through %_par__sret; return void. }
       EmitLine('  ret')
     else
     begin
@@ -7629,8 +7743,12 @@ begin
   if IsFunc then
   begin
     RetQType := QbeTypeOf(ADecl.ResolvedReturnType);
-    if ADecl.ResolvedReturnType.Kind = tyInterface then
+    if (ADecl.ResolvedReturnType.Kind = tyInterface) or
+       ((ADecl.ResolvedReturnType.Kind = tySet) and
+        TSetTypeDesc(ADecl.ResolvedReturnType).IsJumbo()) then
     begin
+      { Interface and jumbo-set returns use a hidden sret pointer (the callee
+        writes the aggregate through it) and return void. }
       if Sig <> '' then Sig := 'l %_par__sret, ' + Sig
       else Sig := 'l %_par__sret';
       EmitLine(Format('%sfunction %s(%s) {', [Prefix, FuncName, Sig]));
@@ -7686,8 +7804,17 @@ begin
               [Par.ParamName, Par.ParamName]));
           end;
         tySet:
-          { w (≤32 members) or l (≤64) bitmask — spill at its width. }
-          if TSetTypeDesc(Par.ResolvedType).BitCount <= 32 then
+          { Small set: w (<=32) / l (<=64) bitmask spilled at its width.
+            Jumbo set: arrives as a pointer; copy into a local bitmap slot. }
+          if TSetTypeDesc(Par.ResolvedType).IsJumbo() then
+          begin
+            EmitLine(Format('  %%_var_%s =l alloc8 %d',
+              [Par.ParamName, TSetTypeDesc(Par.ResolvedType).RawSize()]));
+            EmitLine(Format('  call $memcpy(l %%_var_%s, l %%_par_%s, l %d)',
+              [Par.ParamName, Par.ParamName,
+               TSetTypeDesc(Par.ResolvedType).RawSize()]));
+          end
+          else if TSetTypeDesc(Par.ResolvedType).BitCount <= 32 then
           begin
             EmitLine(Format('  %%_var_%s =l alloc4 1', [Par.ParamName]));
             EmitLine(Format('  storew %%_par_%s, %%_var_%s',
@@ -7775,6 +7902,15 @@ begin
   begin
     if ADecl.ResolvedReturnType.Kind = tyRecord then
       EmitRecordReturnPrologue(TRecordTypeDesc(ADecl.ResolvedReturnType), RC)
+    else if (ADecl.ResolvedReturnType.Kind = tySet) and
+            TSetTypeDesc(ADecl.ResolvedReturnType).IsJumbo() then
+    begin
+      { sret: jumbo-set Result aliases the caller's buffer; zero-init it so a
+        partial build (Include before full assignment) starts empty. }
+      EmitLine('  %_var_Result =l copy %_par__sret');
+      EmitLine(Format('  call $memset(l %%_var_Result, w 0, l %d)',
+        [TSetTypeDesc(ADecl.ResolvedReturnType).RawSize()]));
+    end
     else if ADecl.ResolvedReturnType.Kind = tyInterface then
     begin
       { sret: interface Result is a 16-byte fat pointer (obj+itab) in the
@@ -7858,7 +7994,10 @@ begin
   begin
     if ADecl.ResolvedReturnType.Kind = tyRecord then
       EmitRecordReturnEpilogue(TRecordTypeDesc(ADecl.ResolvedReturnType), RC)
-    else if ADecl.ResolvedReturnType.Kind = tyInterface then
+    else if (ADecl.ResolvedReturnType.Kind = tyInterface) or
+            ((ADecl.ResolvedReturnType.Kind = tySet) and
+             TSetTypeDesc(ADecl.ResolvedReturnType).IsJumbo()) then
+      { sret: the aggregate was written through %_par__sret — return void. }
       EmitLine('  ret')
     else
     begin
@@ -8316,37 +8455,61 @@ begin
   end
   else if UCaseName = 'INCLUDE' then
   begin
-    { Include(S, elem): S := S or (1 shl ord(elem)) }
-    SetQT := QbeTypeOf(TASTExpr(ACall.Args.Items[0]).ResolvedType);
-    SetLoad := LoadInstrFor(TASTExpr(ACall.Args.Items[0]).ResolvedType);
-    SetStore := StoreInstrFor(TASTExpr(ACall.Args.Items[0]).ResolvedType);
-    ArgTemp  := EmitLValueAddr(TASTExpr(ACall.Args.Items[0]));
-    ArgTemp2 := AllocTemp();
-    EmitLine(Format('  %s =%s %s %s', [ArgTemp2, SetQT, SetLoad, ArgTemp]));
-    SizeTemp := EmitExpr(TASTExpr(ACall.Args.Items[1]));
-    ArgLine  := AllocTemp();
-    EmitLine(Format('  %s =%s shl 1, %s', [ArgLine, SetQT, SizeTemp]));
-    SizeTemp := AllocTemp();
-    EmitLine(Format('  %s =%s or %s, %s', [SizeTemp, SetQT, ArgTemp2, ArgLine]));
-    EmitLine(Format('  %s %s, %s', [SetStore, SizeTemp, ArgTemp]));
+    { Jumbo set: in-place bit set via the RTL helper. }
+    if (TASTExpr(ACall.Args.Items[0]).ResolvedType <> nil) and
+       (TASTExpr(ACall.Args.Items[0]).ResolvedType.Kind = tySet) and
+       TSetTypeDesc(TASTExpr(ACall.Args.Items[0]).ResolvedType).IsJumbo() then
+    begin
+      ArgTemp  := EmitLValueAddr(TASTExpr(ACall.Args.Items[0]));
+      SizeTemp := EmitExpr(TASTExpr(ACall.Args.Items[1]));
+      EmitLine(Format('  call $_SetInclude(l %s, w %s)', [ArgTemp, SizeTemp]));
+    end
+    else
+    begin
+      { Include(S, elem): S := S or (1 shl ord(elem)) }
+      SetQT := QbeTypeOf(TASTExpr(ACall.Args.Items[0]).ResolvedType);
+      SetLoad := LoadInstrFor(TASTExpr(ACall.Args.Items[0]).ResolvedType);
+      SetStore := StoreInstrFor(TASTExpr(ACall.Args.Items[0]).ResolvedType);
+      ArgTemp  := EmitLValueAddr(TASTExpr(ACall.Args.Items[0]));
+      ArgTemp2 := AllocTemp();
+      EmitLine(Format('  %s =%s %s %s', [ArgTemp2, SetQT, SetLoad, ArgTemp]));
+      SizeTemp := EmitExpr(TASTExpr(ACall.Args.Items[1]));
+      ArgLine  := AllocTemp();
+      EmitLine(Format('  %s =%s shl 1, %s', [ArgLine, SetQT, SizeTemp]));
+      SizeTemp := AllocTemp();
+      EmitLine(Format('  %s =%s or %s, %s', [SizeTemp, SetQT, ArgTemp2, ArgLine]));
+      EmitLine(Format('  %s %s, %s', [SetStore, SizeTemp, ArgTemp]));
+    end;
   end
   else if UCaseName = 'EXCLUDE' then
   begin
-    { Exclude(S, elem): S := S and (not (1 shl ord(elem))) }
-    SetQT := QbeTypeOf(TASTExpr(ACall.Args.Items[0]).ResolvedType);
-    SetLoad := LoadInstrFor(TASTExpr(ACall.Args.Items[0]).ResolvedType);
-    SetStore := StoreInstrFor(TASTExpr(ACall.Args.Items[0]).ResolvedType);
-    ArgTemp  := EmitLValueAddr(TASTExpr(ACall.Args.Items[0]));
-    ArgTemp2 := AllocTemp();
-    EmitLine(Format('  %s =%s %s %s', [ArgTemp2, SetQT, SetLoad, ArgTemp]));
-    SizeTemp := EmitExpr(TASTExpr(ACall.Args.Items[1]));
-    ArgLine  := AllocTemp();
-    EmitLine(Format('  %s =%s shl 1, %s', [ArgLine, SetQT, SizeTemp]));
-    SizeTemp := AllocTemp();
-    EmitLine(Format('  %s =%s xor %s, -1', [SizeTemp, SetQT, ArgLine]));
-    ArgLine  := AllocTemp();
-    EmitLine(Format('  %s =%s and %s, %s', [ArgLine, SetQT, ArgTemp2, SizeTemp]));
-    EmitLine(Format('  %s %s, %s', [SetStore, ArgLine, ArgTemp]));
+    { Jumbo set: in-place bit clear via the RTL helper. }
+    if (TASTExpr(ACall.Args.Items[0]).ResolvedType <> nil) and
+       (TASTExpr(ACall.Args.Items[0]).ResolvedType.Kind = tySet) and
+       TSetTypeDesc(TASTExpr(ACall.Args.Items[0]).ResolvedType).IsJumbo() then
+    begin
+      ArgTemp  := EmitLValueAddr(TASTExpr(ACall.Args.Items[0]));
+      SizeTemp := EmitExpr(TASTExpr(ACall.Args.Items[1]));
+      EmitLine(Format('  call $_SetExclude(l %s, w %s)', [ArgTemp, SizeTemp]));
+    end
+    else
+    begin
+      { Exclude(S, elem): S := S and (not (1 shl ord(elem))) }
+      SetQT := QbeTypeOf(TASTExpr(ACall.Args.Items[0]).ResolvedType);
+      SetLoad := LoadInstrFor(TASTExpr(ACall.Args.Items[0]).ResolvedType);
+      SetStore := StoreInstrFor(TASTExpr(ACall.Args.Items[0]).ResolvedType);
+      ArgTemp  := EmitLValueAddr(TASTExpr(ACall.Args.Items[0]));
+      ArgTemp2 := AllocTemp();
+      EmitLine(Format('  %s =%s %s %s', [ArgTemp2, SetQT, SetLoad, ArgTemp]));
+      SizeTemp := EmitExpr(TASTExpr(ACall.Args.Items[1]));
+      ArgLine  := AllocTemp();
+      EmitLine(Format('  %s =%s shl 1, %s', [ArgLine, SetQT, SizeTemp]));
+      SizeTemp := AllocTemp();
+      EmitLine(Format('  %s =%s xor %s, -1', [SizeTemp, SetQT, ArgLine]));
+      ArgLine  := AllocTemp();
+      EmitLine(Format('  %s =%s and %s, %s', [ArgLine, SetQT, ArgTemp2, SizeTemp]));
+      EmitLine(Format('  %s %s, %s', [SetStore, ArgLine, ArgTemp]));
+    end;
   end
   else if UCaseName = 'DELETEFILE' then
   begin
@@ -8697,6 +8860,8 @@ var
   DataTemp:     string;
   SQT:          string;
   PMark:        Integer;
+  SetNB:        Integer;   { jumbo set bitmap byte count }
+  SetRS:        Integer;   { jumbo set slot size (RawSize, 8-rounded) }
 begin
   PMark := PendingReleaseMark();
   if AExpr is TFuncCallExpr then
@@ -9856,6 +10021,18 @@ begin
         EmitRecordCallSret(AExpr, SretBuf);
         Exit(SretBuf);
       end;
+      { sret: jumbo-set-returning function — caller allocates a zero-init
+        bitmap buffer and passes its address as the hidden first parameter. }
+      if (MDecl.ResolvedReturnType.Kind = tySet) and
+         TSetTypeDesc(MDecl.ResolvedReturnType).IsJumbo() then
+      begin
+        SetRS   := TSetTypeDesc(MDecl.ResolvedReturnType).RawSize();
+        SretBuf := AllocTemp();
+        EmitLine(Format('  %s =l alloc8 %d', [SretBuf, SetRS]));
+        EmitLine(Format('  call $memset(l %s, w 0, l %d)', [SretBuf, SetRS]));
+        EmitRecordCallSret(AExpr, SretBuf);
+        Exit(SretBuf);
+      end;
       if FC.IsImplicitSelfMethod then
       begin
         ArgTemp := AllocTemp();
@@ -10288,6 +10465,17 @@ begin
       EmitRecordCallSret(AExpr, SretBuf);
       Exit(SretBuf);
     end;
+    { sret: jumbo-set-returning method }
+    if (MDecl.ResolvedReturnType.Kind = tySet) and
+       TSetTypeDesc(MDecl.ResolvedReturnType).IsJumbo() then
+    begin
+      SetRS   := TSetTypeDesc(MDecl.ResolvedReturnType).RawSize();
+      SretBuf := AllocTemp();
+      EmitLine(Format('  %s =l alloc8 %d', [SretBuf, SetRS]));
+      EmitLine(Format('  call $memset(l %s, w 0, l %d)', [SretBuf, SetRS]));
+      EmitRecordCallSret(AExpr, SretBuf);
+      Exit(SretBuf);
+    end;
 
     { Load the object pointer (Self): either from a named variable or from
       evaluating the receiver expression (e.g. a typecast). }
@@ -10675,7 +10863,7 @@ begin
       end
       else
         Ptr := L;
-      if FldAccess.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray] then
+      if IsAggregateAddrType(FldAccess.FieldInfo.TypeDesc) then
         Exit(Ptr);
       QType     := QbeTypeOf(FldAccess.FieldInfo.TypeDesc);
       LoadInstr := LoadInstrFor(FldAccess.FieldInfo.TypeDesc);
@@ -10769,7 +10957,7 @@ begin
       begin
         Exit(Ptr);
       end;
-      if FldAccess.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray] then
+      if IsAggregateAddrType(FldAccess.FieldInfo.TypeDesc) then
         Exit(Ptr);
       QType     := QbeTypeOf(FldAccess.FieldInfo.TypeDesc);
       LoadInstr := LoadInstrFor(FldAccess.FieldInfo.TypeDesc);
@@ -11192,7 +11380,7 @@ begin
         below; without this, passing a class-field record/array by value emitted
         `loadl` of the field address and passed the first 8 bytes as the
         aggregate, crashing the callee.) }
-      if FldAccess.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray] then
+      if IsAggregateAddrType(FldAccess.FieldInfo.TypeDesc) then
         Exit(Ptr);
       QType     := QbeTypeOf(FldAccess.FieldInfo.TypeDesc);
       LoadInstr := LoadInstrFor(FldAccess.FieldInfo.TypeDesc);
@@ -11231,7 +11419,7 @@ begin
       begin
         Exit(Ptr);
       end;
-      if FldAccess.FieldInfo.TypeDesc.Kind in [tyRecord, tyStaticArray] then
+      if IsAggregateAddrType(FldAccess.FieldInfo.TypeDesc) then
         Exit(Ptr);
       QType     := QbeTypeOf(FldAccess.FieldInfo.TypeDesc);
       LoadInstr := LoadInstrFor(FldAccess.FieldInfo.TypeDesc);
@@ -11337,7 +11525,8 @@ begin
     end
     else if TIdentExpr(AExpr).IsConstant and
             ((AExpr.ResolvedType = nil) or
-             (AExpr.ResolvedType.Kind <> tyStaticArray)) then
+             ((AExpr.ResolvedType.Kind <> tyStaticArray) and
+              not IsAggregateAddrType(AExpr.ResolvedType))) then
     begin
       if (AExpr.ResolvedType <> nil) and (AExpr.ResolvedType.Kind = tyString) then
       begin
@@ -11365,7 +11554,7 @@ begin
         from that address (no extra pointer hop). }
       QType := QbeTypeOf(AExpr.ResolvedType);
       if (AExpr.ResolvedType <> nil) and
-         (AExpr.ResolvedType.Kind in [tyRecord, tyStaticArray]) then
+         IsAggregateAddrType(AExpr.ResolvedType) then
       begin
         { Aggregate: %_cap_Name is the storage address — return directly. }
         EmitLine(Format('  %s =l copy %%_cap_%s', [T, TIdentExpr(AExpr).Name]));
@@ -11379,9 +11568,16 @@ begin
         EmitLine(Format('  %s =w loadw %%_cap_%s', [T, TIdentExpr(AExpr).Name]));
       end;
     end
+    else if TIdentExpr(AExpr).ParamMode = pmJumboSetValue then
+    begin
+      { Jumbo set value param: the QBE backend spills it into a local inline
+        bitmap slot (value semantics), so %_var_X IS the bitmap address —
+        return it directly without a load. }
+      Exit(VarRef(TIdentExpr(AExpr).Name, TIdentExpr(AExpr).IsGlobal));
+    end
     else if (TIdentExpr(AExpr).ParamMode <> pmNone) and
             (AExpr.ResolvedType <> nil) and
-            (AExpr.ResolvedType.Kind in [tyRecord, tyStaticArray]) then
+            IsAggregateAddrType(AExpr.ResolvedType) then
     begin
       { Var param of aggregate type: the param slot already holds the address
         of the caller's storage — load and return that as the storage address. }
@@ -11406,7 +11602,7 @@ begin
       Exit('$' + TIdentExpr(AExpr).ConstArraySymbol);
     end
     else if (AExpr.ResolvedType <> nil) and
-            (AExpr.ResolvedType.Kind in [tyRecord, tyStaticArray]) then
+            IsAggregateAddrType(AExpr.ResolvedType) then
     begin
       { Aggregate variable — return its storage address directly (no load). }
       Exit(VarRef(TIdentExpr(AExpr).Name, TIdentExpr(AExpr).IsGlobal));
@@ -11577,20 +11773,80 @@ begin
       end;
       Exit(T);
     end;
-    { Set membership: elem in SetVar — (set >> ord(elem)) & 1 }
+    { Set membership: elem in SetVar }
     if BinExpr.Op = boIn then
     begin
+      { Jumbo set: R is the bitmap address, L the ordinal — _SetIn(R, L). }
+      if (BinExpr.Right.ResolvedType <> nil) and
+         (BinExpr.Right.ResolvedType.Kind = tySet) and
+         TSetTypeDesc(BinExpr.Right.ResolvedType).IsJumbo() then
+      begin
+        EmitLine(Format('  %s =w call $_SetIn(l %s, w %s)', [T, R, L]));
+        Exit(T);
+      end;
+      { Small set: ((set >> ord) & 1) AND (ord < BitCount).  The range guard
+        matters when the set is sized to a literal's max ordinal (e.g.
+        'X in [low members]') but the tested element's ordinal may exceed the
+        set width — a shift past the register width is undefined, so the guard
+        forces a 0 result for out-of-range ordinals. }
       SQT := QbeTypeOf(BinExpr.Right.ResolvedType);
       ArgTemp := AllocTemp();
       EmitLine(Format('  %s =%s shr %s, %s', [ArgTemp, SQT, R, L]));
-      EmitLine(Format('  %s =w and %s, 1', [T, ArgTemp]));
+      T2 := AllocTemp();
+      EmitLine(Format('  %s =w and %s, 1', [T2, ArgTemp]));
+      ArgTemp := AllocTemp();
+      EmitLine(Format('  %s =w csltw %s, %d',
+        [ArgTemp, L, TSetTypeDesc(BinExpr.Right.ResolvedType).BitCount]));
+      EmitLine(Format('  %s =w and %s, %s', [T, T2, ArgTemp]));
       Exit(T);
     end;
 
-    { Set arithmetic: union, difference, intersection }
+    { Set arithmetic: union, difference, intersection, equality }
     if (BinExpr.Left.ResolvedType <> nil) and
        (BinExpr.Left.ResolvedType.Kind = tySet) then
     begin
+      { Jumbo set: L and R are bitmap addresses.  Binary set ops write into a
+        fresh result buffer and return its address; equality returns a w 0/1.
+        NBytes is the (compile-time) bitmap length. }
+      if TSetTypeDesc(BinExpr.Left.ResolvedType).IsJumbo() then
+      begin
+        SetNB := TSetTypeDesc(BinExpr.Left.ResolvedType).RawByteSize();
+        SetRS := TSetTypeDesc(BinExpr.Left.ResolvedType).RawSize();
+        case BinExpr.Op of
+          boAdd:
+          begin
+            EmitLine(Format('  %s =l alloc8 %d', [T, SetRS]));
+            EmitLine(Format('  call $_SetUnion(l %s, l %s, l %s, w %d)',
+              [T, L, R, SetNB]));
+          end;
+          boSub:
+          begin
+            EmitLine(Format('  %s =l alloc8 %d', [T, SetRS]));
+            EmitLine(Format('  call $_SetDiff(l %s, l %s, l %s, w %d)',
+              [T, L, R, SetNB]));
+          end;
+          boMul:
+          begin
+            EmitLine(Format('  %s =l alloc8 %d', [T, SetRS]));
+            EmitLine(Format('  call $_SetInter(l %s, l %s, l %s, w %d)',
+              [T, L, R, SetNB]));
+          end;
+          boEQ:
+            EmitLine(Format('  %s =w call $_SetEqual(l %s, l %s, w %d)',
+              [T, L, R, SetNB]));
+          boNE:
+          begin
+            ArgTemp := AllocTemp();
+            EmitLine(Format('  %s =w call $_SetEqual(l %s, l %s, w %d)',
+              [ArgTemp, L, R, SetNB]));
+            EmitLine(Format('  %s =w ceqw %s, 0', [T, ArgTemp]));
+          end;
+        else
+          raise ECodeGenError.Create(Format(
+            'Operator not supported for set types at line %d', [BinExpr.Line]));
+        end;
+        Exit(T);
+      end;
       SQT := QbeTypeOf(BinExpr.Left.ResolvedType);
       case BinExpr.Op of
         boAdd:  { union: or }
@@ -11918,7 +12174,7 @@ begin
       For scalar types, load through T to get the actual value. }
     T := EmitExpr(TDerefExpr(AExpr).Expr);
     if (AExpr.ResolvedType <> nil) and
-       (AExpr.ResolvedType.Kind in [tyRecord, tyStaticArray]) then
+       IsAggregateAddrType(AExpr.ResolvedType) then
     begin
       { P : ^TRecord — T is already the record's address; no further load }
       Result := T;
@@ -13839,13 +14095,34 @@ end;
 
 function TCodeGenQBE.EmitSetLiteralExpr(AExpr: TArrayLiteralExpr): string;
 var
-  Mask:   Int64;
-  I:      Integer;
-  Elem:   TASTExpr;
-  IdExpr: TIdentExpr;
-  Tmp:    string;
-  QT:     string;
+  Mask:    Int64;
+  I:       Integer;
+  Elem:    TASTExpr;
+  IdExpr:  TIdentExpr;
+  Tmp:     string;
+  QT:      string;
+  ElemVal: string;
 begin
+  { Jumbo set literal: build the bitmap in a fresh stack buffer — memset 0,
+    then set each member's bit via _SetInclude.  Elements may be non-constant
+    (evaluated at runtime), unlike the small-set fast path. }
+  if (AExpr.ResolvedType <> nil) and (AExpr.ResolvedType.Kind = tySet) and
+     TSetTypeDesc(AExpr.ResolvedType).IsJumbo() then
+  begin
+    Tmp := AllocTemp();
+    EmitLine(Format('  %s =l alloc8 %d',
+      [Tmp, TSetTypeDesc(AExpr.ResolvedType).RawSize()]));
+    EmitLine(Format('  call $memset(l %s, w 0, l %d)',
+      [Tmp, TSetTypeDesc(AExpr.ResolvedType).RawSize()]));
+    for I := 0 to AExpr.Elements.Count - 1 do
+    begin
+      Elem    := TASTExpr(AExpr.Elements.Items[I]);
+      ElemVal := EmitExpr(Elem);
+      EmitLine(Format('  call $_SetInclude(l %s, w %s)', [Tmp, ElemVal]));
+    end;
+    Exit(Tmp);
+  end;
+
   Mask := 0;
   for I := 0 to AExpr.Elements.Count - 1 do
   begin
diff --git a/compiler/src/main/pascal/uAST.pas b/compiler/src/main/pascal/uAST.pas
index 028848e..231807e 100644
--- a/compiler/src/main/pascal/uAST.pas
+++ b/compiler/src/main/pascal/uAST.pas
@@ -77,7 +77,8 @@ type
     pmNone,
     pmVar,
     pmRecordValue,
-    pmStaticArrayValue
+    pmStaticArrayValue,
+    pmJumboSetValue       { by-value jumbo (>64) set param: by-ref aggregate ABI }
   );
 
   TIdentExpr = class(TASTExpr)
@@ -271,7 +272,11 @@ type
     { Set iteration path (IsSetIter = True) }
     IsSetIter:            Boolean;
     SetBitCount:          Integer;   { number of bits in the set (= enum member count) }
-    SetMaskVarName:       string;    { synthetic slot holding the evaluated set mask }
+    SetMaskVarName:       string;    { synthetic slot: holds the evaluated set mask
+                                       (small set), or the set's ADDRESS (jumbo) }
+    SetIsJumbo:           Boolean;   { True when the set is >64 members: the slot
+                                       holds a pointer and membership is tested via
+                                       the _SetIn RTL helper, not a register shift }
     destructor Destroy; override;
   end;
 
@@ -585,11 +590,19 @@ type
       declared set type or the set type inferred from the members' enum. }
     IsSet:       Boolean;
     SetElements: TStringList;   { non-nil when IsSet; member ident names }
+    { JUMBO (>64-member) set constant: the bitmap as one decimal byte value per
+      bitmap byte (RawByteSize entries).  Set by uSemantic when IsSet and the
+      set type is jumbo, because the bitmask no longer fits in IntVal (Int64).
+      Nil for small sets (which keep using IntVal). }
+    ConstSetBytes: TStringList;
     { Canonical QBE data-label for an array const, set by uSemantic.  Mangled
       to a unique symbol so identically-named consts in different scopes (and
       RTL-internal consts) do not collide at link time.  Empty for non-array
       consts. }
     ResolvedQbeName: string;
+    { Canonical, mangled QBE data-label for a JUMBO set const's byte blob
+      (mirrors ResolvedQbeName for array consts). Empty otherwise. }
+    ResolvedSetQbeName: string;
     destructor Destroy; override;
   end;
 
@@ -2164,6 +2177,20 @@ begin
   end;
   if ASrc.IntValueExpr <> nil then
     Result.IntValueExpr := CloneExpr(ASrc.IntValueExpr);
+  Result.IsSet := ASrc.IsSet;
+  if ASrc.SetElements <> nil then
+  begin
+    Result.SetElements := TStringList.Create();
+    for I := 0 to ASrc.SetElements.Count - 1 do
+      Result.SetElements.Add(ASrc.SetElements.Strings[I]);
+  end;
+  if ASrc.ConstSetBytes <> nil then
+  begin
+    Result.ConstSetBytes := TStringList.Create();
+    for I := 0 to ASrc.ConstSetBytes.Count - 1 do
+      Result.ConstSetBytes.Add(ASrc.ConstSetBytes.Strings[I]);
+  end;
+  Result.ResolvedSetQbeName := ASrc.ResolvedSetQbeName;
 end;
 
 function CloneMethodParam(ASrc: TMethodParam): TMethodParam;
diff --git a/compiler/src/main/pascal/uSemantic.pas b/compiler/src/main/pascal/uSemantic.pas
index e16e0e1..80b62cd 100644
--- a/compiler/src/main/pascal/uSemantic.pas
+++ b/compiler/src/main/pascal/uSemantic.pas
@@ -240,6 +240,12 @@ type
     function  AnalyseStringSubscriptExpr(AExpr: TStringSubscriptExpr): TTypeDesc;
     function  AnalyseArrayLiteralExpr(AExpr: TArrayLiteralExpr): TTypeDesc;
     function  AnalyseSetLiteralExpr(AExpr: TArrayLiteralExpr; ASetType: TSetTypeDesc): TTypeDesc;
+    { Width (in bits) needed for the anonymous set type of an 'X in [a,b,c]'
+      literal: largest listed member ordinal + 1 when every element is a
+      compile-time enum constant; otherwise the full base-enum member count
+      (conservative).  Keeps low-ordinal membership tests off the jumbo path. }
+    function  SetLiteralBitCount(AExpr: TArrayLiteralExpr;
+                                 ABaseEnum: TEnumTypeDesc): Integer;
     procedure CoerceToCharOrd(ALit: TStringLiteral);
     procedure AnalysePointerWriteStmt(AStmt: TPointerWriteStmt);
     procedure AnalyseStaticSubscriptAssign(AStmt: TStaticSubscriptAssign);
@@ -1887,9 +1893,9 @@ begin
     end;
     if Members.Count = 0 then
       SemanticError('Empty anonymous enumeration in set type', 0, 0);
-    if Members.Count > 64 then
+    if Members.Count > 256 then
       SemanticError(Format(
-        'Anonymous enumeration has %d members; set types support at most 64',
+        'Anonymous enumeration has %d members; set types support at most 256',
         [Members.Count]), 0, 0);
     { Reuse an already-synthesised identical enum: if the first member is a
       defined enum constant whose enum has exactly these members, return it. }
@@ -2042,9 +2048,9 @@ begin
       BaseType := FindTypeOrInstantiate(BaseName);
     if (BaseType <> nil) and (BaseType.Kind = tyEnum) then
     begin
-      if TEnumTypeDesc(BaseType).Members.Count > 64 then
+      if TEnumTypeDesc(BaseType).Members.Count > 256 then
         SemanticError(Format(
-          'Enumeration ''%s'' has %d members; set types support at most 64',
+          'Enumeration ''%s'' has %d members; set types support at most 256',
           [BaseType.Name, TEnumTypeDesc(BaseType).Members.Count]), 0, 0);
       CanonName := 'set of ' + BaseType.Name;
       Result    := FTable.FindType(CanonName);
@@ -3141,12 +3147,17 @@ var
   CanonName: string;
   ExistTD:   TTypeDesc;
   Sym:       TSymbol;
+  Ords:      TStringList;
+  Ord, BIdx, NB, BVal: Integer;
 begin
   Mask     := 0;
   EnumDesc := nil;
+  Ords     := TStringList.Create();
 
-  { Resolve each member to an enum constant; OR its bit into the mask and
-    pin down the shared base enum. }
+  { Resolve each member to an enum constant; record its ordinal and pin down
+    the shared base enum.  The bitmask (small set) or byte bitmap (jumbo set)
+    is built AFTER the set type is known, so we never `shl` by an ordinal >= 64
+    (undefined) before we know whether the set is jumbo. }
   for I := 0 to ACD.SetElements.Count - 1 do
   begin
     MemName := ACD.SetElements.Strings[I];
@@ -3168,7 +3179,7 @@ begin
         [ACD.Name, EnumDesc.Name, MemSym.TypeDesc.Name]), ACD.Line, ACD.Col);
       Exit;
     end;
-    Mask := Mask or (Int64(1) shl MemSym.ConstValue);
+    Ords.Add(IntToStr(MemSym.ConstValue));
   end;
 
   { Determine the set type descriptor. }
@@ -3196,9 +3207,9 @@ begin
   end
   else if EnumDesc <> nil then
   begin
-    if EnumDesc.Members.Count > 64 then
+    if EnumDesc.Members.Count > 256 then
       SemanticError(
-        Format('Enumeration ''%s'' has %d members; set types support at most 64',
+        Format('Enumeration ''%s'' has %d members; set types support at most 256',
           [EnumDesc.Name, EnumDesc.Members.Count]),
         ACD.Line, ACD.Col);
     { Inferred set type: find or create the canonical 'set of <Enum>'. }
@@ -3221,9 +3232,40 @@ begin
     Exit;
   end;
 
-  ACD.IntVal     := Mask;
-  Sym            := TSymbol.Create(ACD.Name, skConstant, SetDesc);
-  Sym.ConstValue := Mask;
+  Sym := TSymbol.Create(ACD.Name, skConstant, SetDesc);
+  if SetDesc.IsJumbo() then
+  begin
+    { Jumbo set const: build a byte-array bitmap; the mask can't fit in Int64. }
+    NB := SetDesc.RawByteSize();
+    ACD.ConstSetBytes := TStringList.Create();
+    for I := 0 to NB - 1 do
+      ACD.ConstSetBytes.Add('0');
+    for I := 0 to Ords.Count - 1 do
+    begin
+      Ord  := StrToInt(Ords.Strings[I]);
+      BIdx := Ord shr 3;
+      BVal := StrToInt(ACD.ConstSetBytes.Strings[BIdx]) or (1 shl (Ord and 7));
+      ACD.ConstSetBytes.Put(BIdx, IntToStr(BVal));
+    end;
+    Sym.ConstSetBytes := TStringList.Create();
+    for I := 0 to ACD.ConstSetBytes.Count - 1 do
+      Sym.ConstSetBytes.Add(ACD.ConstSetBytes.Strings[I]);
+    { Mangled, file-local data label for the bitmap blob (mirrors array
+      consts), shared by the decl and the symbol so reads resolve to it. }
+    if ACD.ResolvedSetQbeName = '' then
+      ACD.ResolvedSetQbeName := Self.NewArrayConstLabel(ACD.Name);
+    Sym.ConstSetQbe := ACD.ResolvedSetQbeName;
+    ACD.IntVal     := 0;
+    Sym.ConstValue := 0;
+  end
+  else
+  begin
+    { Small set: pack into the Int64 bitmask (existing fast path). }
+    for I := 0 to Ords.Count - 1 do
+      Mask := Mask or (Int64(1) shl StrToInt(Ords.Strings[I]));
+    ACD.IntVal     := Mask;
+    Sym.ConstValue := Mask;
+  end;
   if not FTable.Define(Sym) then
     Sym.Free();   { duplicate — cross-unit shadowing tolerated, like scalar consts }
 end;
@@ -3590,9 +3632,9 @@ begin
         SemanticError(
           Format('Set base type ''%s'' must be an enumeration type', [SetDef.BaseTypeName]),
           TD.Line, TD.Col);
-      if TEnumTypeDesc(BaseSym.TypeDesc).Members.Count > 64 then
+      if TEnumTypeDesc(BaseSym.TypeDesc).Members.Count > 256 then
         SemanticError(
-          Format('Enumeration ''%s'' has %d members; set types support at most 64',
+          Format('Enumeration ''%s'' has %d members; set types support at most 256',
             [SetDef.BaseTypeName, TEnumTypeDesc(BaseSym.TypeDesc).Members.Count]),
           TD.Line, TD.Col);
       SetDesc := FTable.NewSetType(TD.Name, TEnumTypeDesc(BaseSym.TypeDesc));
@@ -5595,6 +5637,7 @@ begin
       ForInS.IsSetIter      := True;
       ForInS.ResolvedVarType := ElemType;
       ForInS.SetBitCount    := TSetTypeDesc(CollType).BitCount;
+      ForInS.SetIsJumbo     := TSetTypeDesc(CollType).IsJumbo();
 
       { Inject synthetic mask slot for the evaluated set value }
       ForInS.SetMaskVarName := '__setmask_' + IntToStr(FForInCounter);
@@ -5605,7 +5648,14 @@ begin
       begin
         SynthDecl := TVarDecl.Create();
         SynthDecl.Names.Add(ForInS.SetMaskVarName);
-        if TSetTypeDesc(CollType).BitCount > 32 then
+        if ForInS.SetIsJumbo then
+        begin
+          { Jumbo: the slot holds the set's ADDRESS (pointer-sized), not a mask;
+            membership is tested per-ordinal via the _SetIn RTL helper. }
+          SynthDecl.TypeName    := 'Int64';
+          SynthDecl.ResolvedType := FTable.TypeInt64;
+        end
+        else if TSetTypeDesc(CollType).BitCount > 32 then
         begin
           SynthDecl.TypeName    := 'Int64';
           SynthDecl.ResolvedType := FTable.TypeInt64;
@@ -8709,6 +8759,9 @@ begin
     else if (Sym.Kind = skParameter) and (Sym.TypeDesc <> nil) and
             (Sym.TypeDesc.Kind = tyStaticArray) then
       TIdentExpr(AExpr).ParamMode := pmStaticArrayValue
+    else if (Sym.Kind = skParameter) and (Sym.TypeDesc <> nil) and
+            (Sym.TypeDesc.Kind = tySet) and TSetTypeDesc(Sym.TypeDesc).IsJumbo() then
+      TIdentExpr(AExpr).ParamMode := pmJumboSetValue
     else
       TIdentExpr(AExpr).ParamMode := pmNone;
     TIdentExpr(AExpr).IsGlobal    := Sym.IsGlobal;
@@ -8723,6 +8776,10 @@ begin
       not $Name, to avoid link collisions. }
     if (Sym.ConstArray <> nil) and (Sym.ConstArrayQbe <> '') then
       TIdentExpr(AExpr).ConstArraySymbol := Sym.ConstArrayQbe;
+    { Jumbo set const referenced bare: same mangled-label mechanism — the read
+      resolves to the bitmap blob's address via the aggregate-read path. }
+    if (Sym.ConstSetBytes <> nil) and (Sym.ConstSetQbe <> '') then
+      TIdentExpr(AExpr).ConstArraySymbol := Sym.ConstSetQbe;
     { Bare class type identifier used as a value: metaclass reference.
       The result type is 'class of TFoo'; codegen emits the typeinfo
       address.  Compatibility with untyped Pointer (so 'Pointer(EError)'
@@ -9315,11 +9372,19 @@ begin
   if ABin.Op = boIn then
   begin
     { Coerce array literal [a, b, c] to an anonymous set type when the left
-      operand is an enum — handles the common 'x in [A, B, C]' idiom. }
+      operand is an enum — handles the common 'x in [A, B, C]' idiom.
+      Size the anonymous set by the largest ORDINAL actually listed (when all
+      elements are compile-time enum constants), not the full enum's member
+      count.  This keeps 'Kind in [low members]' on the fast <=64-bit register
+      path even when the base enum has more than 64 members, and only widens to
+      a jumbo set when a listed member's ordinal is itself >= 64.  Elements that
+      are not constant fall back to the full enum size (conservative). }
     if (ABin.Right is TArrayLiteralExpr) and (LType.Kind = tyEnum) then
     begin
       TmpSet := FTable.NewSetType('', TEnumTypeDesc(LType));
       RType := AnalyseSetLiteralExpr(TArrayLiteralExpr(ABin.Right), TmpSet);
+      TmpSet.BitCount := SetLiteralBitCount(TArrayLiteralExpr(ABin.Right),
+        TEnumTypeDesc(LType));
     end;
     if RType.Kind <> tySet then
       SemanticError(
@@ -10122,6 +10187,33 @@ begin
   AExpr.ResolvedType := Result;
 end;
 
+function TSemanticAnalyser.SetLiteralBitCount(AExpr: TArrayLiteralExpr;
+  ABaseEnum: TEnumTypeDesc): Integer;
+var
+  I, MaxOrd: Integer;
+  Elem: TASTExpr;
+begin
+  MaxOrd := -1;
+  for I := 0 to AExpr.Elements.Count - 1 do
+  begin
+    Elem := TASTExpr(AExpr.Elements.Items[I]);
+    { Only compile-time enum constants have a known ordinal.  Any non-constant
+      element forces the conservative full-enum width. }
+    if (Elem is TIdentExpr) and TIdentExpr(Elem).IsConstant then
+    begin
+      if TIdentExpr(Elem).ConstValue > MaxOrd then
+        MaxOrd := TIdentExpr(Elem).ConstValue;
+    end
+    else
+      Exit(ABaseEnum.Members.Count);
+  end;
+  { Empty literal -> width 1 (a single zero byte fits any small set). }
+  if MaxOrd < 0 then
+    Result := 1
+  else
+    Result := MaxOrd + 1;
+end;
+
 function TSemanticAnalyser.AnalyseSetLiteralExpr(AExpr: TArrayLiteralExpr;
   ASetType: TSetTypeDesc): TTypeDesc;
 { Validates a set literal [elem, ...] against ASetType.
diff --git a/compiler/src/main/pascal/uSymbolTable.pas b/compiler/src/main/pascal/uSymbolTable.pas
index 3c7b428..d33809d 100644
--- a/compiler/src/main/pascal/uSymbolTable.pas
+++ b/compiler/src/main/pascal/uSymbolTable.pas
@@ -124,12 +124,25 @@ type
   end;
 
   { Set type descriptor.  BaseType is the element enum; BitCount is the number
-    of bits required (= BaseType.Members.Count).  Stored as QBE 'w' for ≤32
-    members, 'l' for 33–64.  Each member ordinal N maps to bit (1 shl N). }
+    of bits required (= BaseType.Members.Count).  Each member ordinal N maps to
+    bit N of the bitmap.  Representation depends on BitCount:
+      BitCount <= 32  -> QBE 'w' (32-bit register), bit (1 shl N)
+      BitCount <= 64  -> QBE 'l' (64-bit register), bit (1 shl N)
+      BitCount  > 64  -> JUMBO: an inline byte-array bitmap of RawByteSize
+                          bytes, treated as an aggregate (like a record): bit N
+                          lives at byte (N shr 3), mask (1 shl (N and 7)).
+                          Operated on via the _Set* RTL helpers, never a single
+                          register.  Max 256 members -> 32 bytes. }
   TSetTypeDesc = class(TTypeDesc)
   public
     [Unretained] BaseType: TEnumTypeDesc;  { not owned }
     BitCount: Integer;        { = BaseType.Members.Count }
+    { True when this set is too wide for a single 64-bit register and must use
+      the inline byte-array (aggregate) representation + _Set* RTL helpers. }
+    function IsJumbo: Boolean;
+    { Number of bitmap bytes for the jumbo representation = ceil(BitCount/8).
+      Only meaningful when IsJumbo; <= 32 for the 256-member ceiling. }
+    function RawByteSize: Integer;
   end;
 
   { One parameter of a procedural type signature. }
@@ -336,6 +349,12 @@ type
     ConstArray:  TStringList; { owned; non-nil for array-typed const; raw element values }
     ConstArrayQbe: string;    { canonical QBE data-label for an array const; mangled
                                 to avoid collisions across scopes and with the RTL }
+    ConstSetBytes: TStringList; { owned; non-nil for a JUMBO (>64-member) set
+                                  const; one decimal byte value per bitmap byte
+                                  (RawByteSize entries).  Small sets keep using
+                                  ConstValue (the Int64 mask) instead. }
+    ConstSetQbe: string;      { canonical, mangled QBE data-label for a jumbo set
+                                const's byte blob (mirrors ConstArrayQbe) }
     IsWeak:     Boolean;      { true for variables declared [Weak]; codegen
                                 keys off this to emit _WeakAssign instead
                                 of the strong addref/release pattern. }
@@ -627,6 +646,16 @@ begin
   Result := Kind = tyRecord;
 end;
 
+function TSetTypeDesc.IsJumbo: Boolean;
+begin
+  Result := BitCount > 64;
+end;
+
+function TSetTypeDesc.RawByteSize: Integer;
+begin
+  Result := (BitCount + 7) div 8;
+end;
+
 function TTypeDesc.RawSize: Integer;
 begin
   case Kind of
@@ -636,7 +665,10 @@ begin
     tyInt64, tyUInt64, tyString, tyClass, tyPointer, tyNil, tyDouble: Result := 8;
     tySingle: Result := 4;
     tyRecord: Result := TRecordTypeDesc(Self).TotalSize();
-    tySet: if TSetTypeDesc(Self).BitCount <= 32 then Result := 4 else Result := 8;
+    tySet:
+      if TSetTypeDesc(Self).BitCount <= 32 then Result := 4
+      else if TSetTypeDesc(Self).BitCount <= 64 then Result := 8
+      else Result := (TSetTypeDesc(Self).RawByteSize() + 7) and (not 7);
     tyStaticArray:
       Result := (TStaticArrayTypeDesc(Self).HighBound -
                  TStaticArrayTypeDesc(Self).LowBound + 1) *
@@ -662,7 +694,10 @@ begin
     tyNil:               Result := 8;
     tyDouble:            Result := 8;
     tySingle:            Result := 4;
-    tySet: if TSetTypeDesc(Self).BitCount <= 32 then Result := 4 else Result := 8;
+    tySet:
+      if TSetTypeDesc(Self).BitCount <= 32 then Result := 4
+      else if TSetTypeDesc(Self).BitCount <= 64 then Result := 8
+      else Result := (TSetTypeDesc(Self).RawByteSize() + 7) and (not 7);
     tyStaticArray:
       Result := (TStaticArrayTypeDesc(Self).HighBound -
                  TStaticArrayTypeDesc(Self).LowBound + 1) *
@@ -685,6 +720,8 @@ begin
     tySingle:            Result := 4;
     tyInt64, tyUInt64, tyString:   Result := 8;
     tyRecord:            Result := TRecordTypeDesc(Self).MaxAlign();
+    { Sets: 4-byte alignment for the 32-bit register form, else 8 (the 64-bit
+      register form and the jumbo byte-array, which we keep 8-aligned). }
     tySet: if TSetTypeDesc(Self).BitCount <= 32 then Result := 4 else Result := 8;
     tyStaticArray: Result := TStaticArrayTypeDesc(Self).ElementType.AllocAlign();
   else
diff --git a/compiler/src/test/pascal/TestRunner.pas b/compiler/src/test/pascal/TestRunner.pas
index 0bf5c79..c264649 100644
--- a/compiler/src/test/pascal/TestRunner.pas
+++ b/compiler/src/test/pascal/TestRunner.pas
@@ -72,6 +72,8 @@ uses
   cp.test.defaultargs,
   cp.test.caseenum,
   cp.test.sets,
+  cp.test.jumboset,
+  cp.test.e2e.jumboset,
   cp.test.selfhosting,
   cp.test.process,
   cp.test.openarray,
diff --git a/compiler/src/test/pascal/cp.test.e2e.jumboset.pas b/compiler/src/test/pascal/cp.test.e2e.jumboset.pas
new file mode 100644
index 0000000..4864054
--- /dev/null
+++ b/compiler/src/test/pascal/cp.test.e2e.jumboset.pas
@@ -0,0 +1,170 @@
+{
+  Blaise - An Object Pascal Compiler
+  Copyright (c) 2026 Graeme Geldenhuys
+  SPDX-License-Identifier: Apache-2.0 WITH Swift-exception
+  Licensed under the Apache License v2.0 with Runtime Library Exception.
+  See LICENSE file in the project root for full license terms.
+}
+
+unit cp.test.e2e.jumboset;
+
+{ E2E tests for JUMBO sets (set of an enum with >64 members): compile -> run,
+  assert stdout, on BOTH backends (QBE + native) via AssertRunsOnAll.  Covers
+  membership across the >64 boundary, Include/Exclude, union/intersection/
+  difference, equality, for-in, value params, sret returns, and a jumbo
+  constant consumed at runtime. }
+
+interface
+
+uses
+  classes, blaise.testing, cp.test.e2e.base;
+
+type
+  [Threaded]
+  TE2EJumboSetTests = class(TE2ETestCase)
+  protected
+    procedure SetUp; override;
+  published
+    procedure TestRun_IncludeMembership_AcrossBoundary;
+    procedure TestRun_SetOps_UnionInterDiff;
+    procedure TestRun_Equality;
+    procedure TestRun_ForIn_CountsMembers;
+    procedure TestRun_Param_And_Return;
+    procedure TestRun_Constant;
+  end;
+
+implementation
+
+const
+  LE = #10;
+
+  { 80-member enum shared by the test programs. }
+  ENUMHDR =
+    '''
+    type TBig = (b00,b01,b02,b03,b04,b05,b06,b07,b08,b09,b10,b11,b12,b13,b14,b15,
+                 b16,b17,b18,b19,b20,b21,b22,b23,b24,b25,b26,b27,b28,b29,b30,b31,
+                 b32,b33,b34,b35,b36,b37,b38,b39,b40,b41,b42,b43,b44,b45,b46,b47,
+                 b48,b49,b50,b51,b52,b53,b54,b55,b56,b57,b58,b59,b60,b61,b62,b63,
+                 b64,b65,b66,b67,b68,b69,b70,b71,b72,b73,b74,b75,b76,b77,b78,b79);
+         TBigSet = set of TBig;
+    ''';
+
+procedure TE2EJumboSetTests.SetUp;
+begin
+  inherited SetUp();
+  SetUpScratch('compiler/target/test-e2e-jumboset');
+end;
+
+procedure TE2EJumboSetTests.TestRun_IncludeMembership_AcrossBoundary;
+var Src: string;
+begin
+  if not ToolchainAvailable() then begin Ignore('toolchain unavailable'); Exit end;
+  Src := 'program P;' + LE + ENUMHDR + LE +
+         'var s: TBigSet;' + LE +
+         'begin' + LE +
+         '  s := [];' + LE +
+         '  Include(s, b70);' + LE +
+         '  Include(s, b05);' + LE +
+         '  WriteLn(b70 in s);' + LE +   { True }
+         '  WriteLn(b71 in s);' + LE +   { False }
+         '  WriteLn(b05 in s);' + LE +   { True }
+         '  Exclude(s, b70);' + LE +
+         '  WriteLn(b70 in s)' + LE +    { False }
+         'end.';
+  AssertRunsOnAll(Src, 'True' + LE + 'False' + LE + 'True' + LE + 'False' + LE, 0);
+end;
+
+procedure TE2EJumboSetTests.TestRun_SetOps_UnionInterDiff;
+var Src: string;
+begin
+  if not ToolchainAvailable() then begin Ignore('toolchain unavailable'); Exit end;
+  Src := 'program P;' + LE + ENUMHDR + LE +
+         'var a, b, c: TBigSet;' + LE +
+         'begin' + LE +
+         '  a := [b05, b70];' + LE +
+         '  b := [b05, b40];' + LE +
+         '  c := a + b;' + LE +
+         '  WriteLn(b05 in c, b40 in c, b70 in c);' + LE +  { True True True }
+         '  c := a * b;' + LE +
+         '  WriteLn(b05 in c, b40 in c, b70 in c);' + LE +  { True False False }
+         '  c := a - b;' + LE +
+         '  WriteLn(b05 in c, b70 in c)' + LE +             { False True }
+         'end.';
+  AssertRunsOnAll(Src,
+    'TrueTrueTrue' + LE + 'TrueFalseFalse' + LE + 'FalseTrue' + LE, 0);
+end;
+
+procedure TE2EJumboSetTests.TestRun_Equality;
+var Src: string;
+begin
+  if not ToolchainAvailable() then begin Ignore('toolchain unavailable'); Exit end;
+  Src := 'program P;' + LE + ENUMHDR + LE +
+         'var a, b: TBigSet;' + LE +
+         'begin' + LE +
+         '  a := [b70, b05];' + LE +
+         '  b := [b05, b70];' + LE +
+         '  WriteLn(a = b);' + LE +      { True }
+         '  Include(b, b79);' + LE +
+         '  WriteLn(a = b);' + LE +      { False }
+         '  WriteLn(a <> b)' + LE +      { True }
+         'end.';
+  AssertRunsOnAll(Src, 'True' + LE + 'False' + LE + 'True' + LE, 0);
+end;
+
+procedure TE2EJumboSetTests.TestRun_ForIn_CountsMembers;
+var Src: string;
+begin
+  if not ToolchainAvailable() then begin Ignore('toolchain unavailable'); Exit end;
+  Src := 'program P;' + LE + ENUMHDR + LE +
+         'var s: TBigSet; e: TBig; n: Integer;' + LE +
+         'begin' + LE +
+         '  s := [b05, b40, b70, b79];' + LE +
+         '  n := 0;' + LE +
+         '  for e in s do n := n + 1;' + LE +
+         '  WriteLn(n);' + LE +          { 4 }
+         '  for e in s do Write(Ord(e), '' '');' + LE +
+         '  WriteLn' + LE +
+         'end.';
+  AssertRunsOnAll(Src, '4' + LE + '5 40 70 79 ' + LE, 0);
+end;
+
+procedure TE2EJumboSetTests.TestRun_Param_And_Return;
+var Src: string;
+begin
+  if not ToolchainAvailable() then begin Ignore('toolchain unavailable'); Exit end;
+  Src := 'program P;' + LE + ENUMHDR + LE +
+         'function HasHigh(const x: TBigSet): Boolean;' + LE +
+         'begin Result := b70 in x; end;' + LE +
+         'function MakeSet: TBigSet;' + LE +
+         'begin Result := [b65, b70]; end;' + LE +
+         'var s: TBigSet;' + LE +
+         'begin' + LE +
+         '  s := [b70, b05];' + LE +
+         '  WriteLn(HasHigh(s));' + LE +    { True }
+         '  s := [b05];' + LE +
+         '  WriteLn(HasHigh(s));' + LE +    { False }
+         '  s := MakeSet();' + LE +
+         '  WriteLn(b65 in s, b70 in s, b05 in s)' + LE +  { True True False }
+         'end.';
+  AssertRunsOnAll(Src,
+    'True' + LE + 'False' + LE + 'TrueTrueFalse' + LE, 0);
+end;
+
+procedure TE2EJumboSetTests.TestRun_Constant;
+var Src: string;
+begin
+  if not ToolchainAvailable() then begin Ignore('toolchain unavailable'); Exit end;
+  Src := 'program P;' + LE + ENUMHDR + LE +
+         'const HIGHS: TBigSet = [b65, b70, b79];' + LE +
+         'var s: TBigSet;' + LE +
+         'begin' + LE +
+         '  s := HIGHS;' + LE +
+         '  WriteLn(b65 in s, b70 in s, b79 in s, b00 in s)' + LE +  { True True True False }
+         'end.';
+  AssertRunsOnAll(Src, 'TrueTrueTrueFalse' + LE, 0);
+end;
+
+initialization
+  RegisterTest(TE2EJumboSetTests);
+
+end.
diff --git a/compiler/src/test/pascal/cp.test.jumboset.pas b/compiler/src/test/pascal/cp.test.jumboset.pas
new file mode 100644
index 0000000..0b6bd6d
--- /dev/null
+++ b/compiler/src/test/pascal/cp.test.jumboset.pas
@@ -0,0 +1,189 @@
+{
+  Blaise - An Object Pascal Compiler
+  Copyright (c) 2026 Graeme Geldenhuys
+  SPDX-License-Identifier: Apache-2.0 WITH Swift-exception
+  Licensed under the Apache License v2.0 with Runtime Library Exception.
+  See LICENSE file in the project root for full license terms.
+}
+
+unit cp.test.jumboset;
+
+{ IR unit tests for JUMBO sets — `set of <enum>` whose enum has more than 64
+  members (up to the 256 ceiling).  Jumbo sets are inline byte-array bitmaps
+  operated on via the _Set* RTL helpers, unlike <=64-member sets which stay in
+  a w/l register.  These tests assert the generated QBE IR routes jumbo set
+  operations to the helper calls and that a <=64 set in the same file still
+  uses the register path (regression). }
+
+interface
+
+uses
+  Classes, SysUtils, blaise.testing,
+  uLexer, uParser, uAST, uSymbolTable, uSemantic, blaise.codegen.qbe;
+
+type
+  TJumboSetTests = class(TTestCase)
+  private
+    function GenIR(const ASrc: string): string;
+  published
+    procedure TestSlot_SizedToBitmap;
+    procedure TestZeroInit_UsesMemset;
+    procedure TestIn_CallsSetIn;
+    procedure TestUnion_CallsSetUnion;
+    procedure TestInter_CallsSetInter;
+    procedure TestDiff_CallsSetDiff;
+    procedure TestEqual_CallsSetEqual;
+    procedure TestInclude_CallsSetInclude;
+    procedure TestExclude_CallsSetExclude;
+    procedure TestAssignment_UsesMemcpy;
+    procedure TestConst_EmitsByteBlob;
+    procedure TestSmallSet_StillUsesRegister;
+  end;
+
+implementation
+
+const
+  { An 80-member enum (b00..b79) — clears the 64 boundary cheaply. }
+  EnumDecl =
+    '  TBig = (b00,b01,b02,b03,b04,b05,b06,b07,b08,b09,b10,b11,b12,b13,b14,b15,' + #10 +
+    '          b16,b17,b18,b19,b20,b21,b22,b23,b24,b25,b26,b27,b28,b29,b30,b31,' + #10 +
+    '          b32,b33,b34,b35,b36,b37,b38,b39,b40,b41,b42,b43,b44,b45,b46,b47,' + #10 +
+    '          b48,b49,b50,b51,b52,b53,b54,b55,b56,b57,b58,b59,b60,b61,b62,b63,' + #10 +
+    '          b64,b65,b66,b67,b68,b69,b70,b71,b72,b73,b74,b75,b76,b77,b78,b79);' + #10 +
+    '  TBigSet = set of TBig;' + #10;
+
+function TJumboSetTests.GenIR(const ASrc: string): string;
+var
+  Lex:  TLexer;
+  Par:  TParser;
+  SA:   TSemanticAnalyser;
+  CG:   TCodeGenQBE;
+  Prog: TProgram;
+begin
+  Lex  := TLexer.Create(ASrc);
+  Par  := TParser.Create(Lex);
+  Prog := Par.Parse();
+  Par.Free(); Lex.Free();
+  SA   := TSemanticAnalyser.Create();
+  SA.Analyse(Prog);
+  SA.Free();
+  CG   := TCodeGenQBE.Create();
+  CG.Generate(Prog);
+  Result := CG.GetOutput();
+  CG.Free();
+  Prog.Free();
+end;
+
+procedure TJumboSetTests.TestSlot_SizedToBitmap;
+var IR: string;
+begin
+  { 80 bits -> 10 bytes -> rounded to 16: the global slot is a 16-byte blob. }
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'var s: TBigSet;' + #10 + 'begin end.');
+  AssertTrue('jumbo global emits a 16-byte zero blob',
+    Pos('$s = { z 16 }', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestZeroInit_UsesMemset;
+var IR: string;
+begin
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'procedure Q; var s: TBigSet; begin s := []; end;' + #10 +
+              'begin end.');
+  AssertTrue('jumbo local zero-init via memset', Pos('call $memset', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestIn_CallsSetIn;
+var IR: string;
+begin
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'var s: TBigSet; b: Boolean;' + #10 +
+              'begin b := b70 in s; end.');
+  AssertTrue('jumbo in -> _SetIn', Pos('call $_SetIn(', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestUnion_CallsSetUnion;
+var IR: string;
+begin
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'var a, b, c: TBigSet;' + #10 + 'begin c := a + b; end.');
+  AssertTrue('jumbo + -> _SetUnion', Pos('call $_SetUnion(', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestInter_CallsSetInter;
+var IR: string;
+begin
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'var a, b, c: TBigSet;' + #10 + 'begin c := a * b; end.');
+  AssertTrue('jumbo * -> _SetInter', Pos('call $_SetInter(', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestDiff_CallsSetDiff;
+var IR: string;
+begin
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'var a, b, c: TBigSet;' + #10 + 'begin c := a - b; end.');
+  AssertTrue('jumbo - -> _SetDiff', Pos('call $_SetDiff(', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestEqual_CallsSetEqual;
+var IR: string;
+begin
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'var a, b: TBigSet; x: Boolean;' + #10 +
+              'begin x := a = b; end.');
+  AssertTrue('jumbo = -> _SetEqual', Pos('call $_SetEqual(', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestInclude_CallsSetInclude;
+var IR: string;
+begin
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'var s: TBigSet;' + #10 + 'begin Include(s, b70); end.');
+  AssertTrue('jumbo Include -> _SetInclude', Pos('call $_SetInclude(', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestExclude_CallsSetExclude;
+var IR: string;
+begin
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'var s: TBigSet;' + #10 + 'begin Exclude(s, b70); end.');
+  AssertTrue('jumbo Exclude -> _SetExclude', Pos('call $_SetExclude(', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestAssignment_UsesMemcpy;
+var IR: string;
+begin
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'var a, b: TBigSet;' + #10 + 'begin a := b; end.');
+  AssertTrue('jumbo assignment via memcpy', Pos('call $memcpy', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestConst_EmitsByteBlob;
+var IR: string;
+begin
+  IR := GenIR('program P;' + #10 + 'type' + #10 + EnumDecl +
+              'const H: TBigSet = [b65, b70, b79];' + #10 +
+              'var s: TBigSet;' + #10 + 'begin s := H; end.');
+  { 80-bit bitmap blob: a data item of `b` bytes; byte 8 holds bits for 65,70. }
+  AssertTrue('jumbo const emits a byte blob', Pos('data $', IR) >= 0);
+  AssertTrue('blob contains byte directives', Pos('b 66', IR) >= 0);
+end;
+
+procedure TJumboSetTests.TestSmallSet_StillUsesRegister;
+var IR: string;
+begin
+  { A <=64 set in the same shape must NOT use the _Set* helpers — it stays a
+    register bitmask. }
+  IR := GenIR('program P;' + #10 +
+              'type TSmall = (s0,s1,s2,s3); TSmallSet = set of TSmall;' + #10 +
+              'var s: TSmallSet; b: Boolean;' + #10 +
+              'begin s := [s1]; b := s1 in s; end.');
+  AssertTrue('small set does not call _SetIn', Pos('call $_SetIn', IR) < 0);
+  AssertTrue('small set does not call _SetUnion', Pos('call $_SetUnion', IR) < 0);
+end;
+
+initialization
+  RegisterTest(TJumboSetTests);
+
+end.
diff --git a/compiler/src/test/pascal/cp.test.sets.pas b/compiler/src/test/pascal/cp.test.sets.pas
index c3f0f58..1813d24 100644
--- a/compiler/src/test/pascal/cp.test.sets.pas
+++ b/compiler/src/test/pascal/cp.test.sets.pas
@@ -100,7 +100,7 @@ type
     { 64-bit sets (>32 members)                                            }
     { ------------------------------------------------------------------ }
     procedure TestSemantic_Set64_TypeRegistered;
-    procedure TestSemantic_Set64_TooManyMembers_Fails;
+    procedure TestSemantic_Set_Over256Members_Fails;
     procedure TestCodegen_Set64_VarAllocsEmitsLongZero;
     procedure TestCodegen_Set64_LiteralEmitsLongMask;
     procedure TestCodegen_Set64_InOperatorUsesLong;
@@ -549,15 +549,39 @@ const
     program P;
     type
       THuge = (
-        A00, A01, A02, A03, A04, A05, A06, A07,
-        A08, A09, A10, A11, A12, A13, A14, A15,
-        A16, A17, A18, A19, A20, A21, A22, A23,
-        A24, A25, A26, A27, A28, A29, A30, A31,
-        A32, A33, A34, A35, A36, A37, A38, A39,
-        A40, A41, A42, A43, A44, A45, A46, A47,
-        A48, A49, A50, A51, A52, A53, A54, A55,
-        A56, A57, A58, A59, A60, A61, A62, A63,
-        A64);
+        A000, A001, A002, A003, A004, A005, A006, A007,
+        A008, A009, A010, A011, A012, A013, A014, A015,
+        A016, A017, A018, A019, A020, A021, A022, A023,
+        A024, A025, A026, A027, A028, A029, A030, A031,
+        A032, A033, A034, A035, A036, A037, A038, A039,
+        A040, A041, A042, A043, A044, A045, A046, A047,
+        A048, A049, A050, A051, A052, A053, A054, A055,
+        A056, A057, A058, A059, A060, A061, A062, A063,
+        A064, A065, A066, A067, A068, A069, A070, A071,
+        A072, A073, A074, A075, A076, A077, A078, A079,
+        A080, A081, A082, A083, A084, A085, A086, A087,
+        A088, A089, A090, A091, A092, A093, A094, A095,
+        A096, A097, A098, A099, A100, A101, A102, A103,
+        A104, A105, A106, A107, A108, A109, A110, A111,
+        A112, A113, A114, A115, A116, A117, A118, A119,
+        A120, A121, A122, A123, A124, A125, A126, A127,
+        A128, A129, A130, A131, A132, A133, A134, A135,
+        A136, A137, A138, A139, A140, A141, A142, A143,
+        A144, A145, A146, A147, A148, A149, A150, A151,
+        A152, A153, A154, A155, A156, A157, A158, A159,
+        A160, A161, A162, A163, A164, A165, A166, A167,
+        A168, A169, A170, A171, A172, A173, A174, A175,
+        A176, A177, A178, A179, A180, A181, A182, A183,
+        A184, A185, A186, A187, A188, A189, A190, A191,
+        A192, A193, A194, A195, A196, A197, A198, A199,
+        A200, A201, A202, A203, A204, A205, A206, A207,
+        A208, A209, A210, A211, A212, A213, A214, A215,
+        A216, A217, A218, A219, A220, A221, A222, A223,
+        A224, A225, A226, A227, A228, A229, A230, A231,
+        A232, A233, A234, A235, A236, A237, A238, A239,
+        A240, A241, A242, A243, A244, A245, A246, A247,
+        A248, A249, A250, A251, A252, A253, A254, A255,
+        A256);
       THugeSet = set of THuge;
     begin
     end.
@@ -1069,8 +1093,10 @@ begin
   SemanticOK(SrcSet64TypeDecl);
 end;
 
-procedure TSetTests.TestSemantic_Set64_TooManyMembers_Fails;
+procedure TSetTests.TestSemantic_Set_Over256Members_Fails;
 begin
+  { 257 members exceeds the 256 ceiling — the largest set Blaise supports
+    (a jumbo byte-array bitmap of up to 32 bytes). }
   SemanticFail(SrcSetTooManyMembers);
 end;
 
diff --git a/docs/grammar.ebnf b/docs/grammar.ebnf
index f30fc82..9403631 100644
--- a/docs/grammar.ebnf
+++ b/docs/grammar.ebnf
@@ -647,11 +647,16 @@ SetType
     = SET OF ( IDENT | EnumDef )
     ;
 
-(* The base enumeration must have at most 64 members.  Sets with up to 32
- * members occupy 4 bytes (QBE 'w'); sets with 33–64 members occupy 8 bytes
- * (QBE 'l').  Each member ordinal N maps to bit (1 shl N) in the bitmask.
- * Enumerations with more than 64 members are rejected by the semantic
- * analyser — extending to 256 (byte-array sets) is a future goal. *)
+(* The base enumeration must have at most 256 members.  Storage scales with the
+ * member count:
+ *   <= 32 members : 4 bytes, a QBE 'w' register bitmask
+ *   <= 64 members : 8 bytes, a QBE 'l' register bitmask
+ *   <= 256 members: an inline byte-array bitmap of ceil(N/8) bytes (a "jumbo"
+ *                   set), operated on via the _Set* RTL helpers like an
+ *                   aggregate (record/static array)
+ * Member ordinal N maps to bit (N mod 8) of byte (N div 8) in all forms.
+ * Enumerations with more than 256 members are rejected by the semantic
+ * analyser (256 is the classic Pascal maximum, matching a byte-indexed set). *)
 
 (* Procedural type — bare or method pointer.
  *
diff --git a/docs/language-rationale.adoc b/docs/language-rationale.adoc
index 12378f3..19fc853 100644
--- a/docs/language-rationale.adoc
+++ b/docs/language-rationale.adoc
@@ -1280,16 +1280,45 @@ bitmask in which bit N is set when the enum member with ordinal N is included.
 
 ==== Storage model
 
-- ≤ 32 enum members: stored as a single QBE `w` (32-bit word).
-- 33–64 members: stored as a single QBE `l` (64-bit long).
-- More than 64 members: rejected by the semantic analyser.  QBE has no 128-bit
-  integer type, so supporting 65–256 elements would require a byte-array
-  representation — deferred until a real use case arises.  FPC/Delphi support
-  up to 256 with a 32-byte fixed-size set, but 64 covers the vast majority of
-  real-world enum sets.
+Storage scales with the enum member count, so the common small-set case stays a
+single fast machine register and larger sets remain correct:
 
+- ≤ 32 enum members: a single QBE `w` (32-bit word) register bitmask.
+- 33–64 members: a single QBE `l` (64-bit long) register bitmask.
+- 65–256 members ("jumbo" sets): an inline byte-array bitmap of `ceil(N/8)`
+  bytes (≤ 32 for the 256-member ceiling).  QBE has no integer type wider than
+  `l`, so a jumbo set cannot live in one register; it is treated as a value
+  aggregate (like a record or static array) — passed by reference, returned via
+  sret, zero-initialised with `memset`, copied with `memcpy` — and its
+  operations (`in`, `+`, `-`, `*`, `=`, `<>`, `Include`, `Exclude`, `for..in`)
+  are performed by the `_Set*` RTL helpers in `blaise_set.pas` rather than
+  inline register instructions.
+- More than 256 members: rejected by the semantic analyser.  256 is the classic
+  Pascal maximum — a byte-indexed set covering ordinals 0..255 — matching FPC's
+  32-byte fixed-size set.
+
+In every form, member ordinal N occupies bit `N mod 8` of byte `N div 8`, so
+the bitmap layout is identical whether the set lives in a register or memory.
 Sets are value types (copied on assignment), not heap-allocated.
 
+The Java `EnumSet` design is the closest analogue: ≤ 64 members use a single
+machine word (`RegularEnumSet`), and a wider universe transparently switches to
+a multi-word bitmap (`JumboEnumSet`) with the same operations applied across the
+words.
+
+==== Set literal sizing (`X in [a, b, c]`)
+
+The anonymous set type synthesised for an `in`-literal is sized to the **largest
+ordinal actually listed** (when every element is a compile-time constant), not
+the base enum's full member count.  So `Token in [tkBegin, tkEnd]` over an
+86-member token enum stays a fast register set, and only widens to a jumbo set
+if a listed member's own ordinal is ≥ 64.  The register membership test carries
+a range guard so that testing an element whose ordinal exceeds the set's width
+correctly yields `False` (rather than relying on an out-of-range shift).  This
+keeps the compiler's own pervasive `Kind in [...]` token tests off the jumbo
+path and avoids a latent miscompile that the old fixed-`l` representation hid
+(any listed ordinal ≥ 64 was silently dropped).
+
 ==== Set literals and disambiguation
 
 Set literals use the same `[elem, ...]` bracket notation as array literals.
diff --git a/runtime/Makefile b/runtime/Makefile
index 076cee7..8565ae4 100644
--- a/runtime/Makefile
+++ b/runtime/Makefile
@@ -34,6 +34,7 @@ ASM_OBJS = $(OBJ_DIR)/blaise_setjmp_x86_64.o \
 # Pascal RTL units compiled via the Blaise compiler.
 PAS_OBJS = $(OBJ_DIR)/blaise_mem.o \
            $(OBJ_DIR)/blaise_str.o \
+           $(OBJ_DIR)/blaise_set.o \
            $(OBJ_DIR)/blaise_arc.o \
            $(OBJ_DIR)/blaise_weak.o \
            $(OBJ_DIR)/blaise_float.o \
@@ -64,6 +65,10 @@ $(OBJ_DIR)/blaise_str.o: $(PAS_SRC_DIR)/blaise_str.pas
 	@mkdir -p $(OBJ_DIR)
 	$(BLAISE) --source $< --unit-path $(PAS_SRC_DIR) --output $@
 
+$(OBJ_DIR)/blaise_set.o: $(PAS_SRC_DIR)/blaise_set.pas
+	@mkdir -p $(OBJ_DIR)
+	$(BLAISE) --source $< --unit-path $(PAS_SRC_DIR) --output $@
+
 $(OBJ_DIR)/blaise_arc.o: $(PAS_SRC_DIR)/blaise_arc.pas
 	@mkdir -p $(OBJ_DIR)
 	$(BLAISE) --source $< --unit-path $(PAS_SRC_DIR) --output $@
diff --git a/runtime/src/main/pascal/blaise_set.pas b/runtime/src/main/pascal/blaise_set.pas
new file mode 100644
index 0000000..ba9eecb
--- /dev/null
+++ b/runtime/src/main/pascal/blaise_set.pas
@@ -0,0 +1,164 @@
+{
+  Blaise - An Object Pascal Compiler
+  Copyright (c) 2026 Graeme Geldenhuys
+  SPDX-License-Identifier: Apache-2.0 WITH Swift-exception
+  Licensed under the Apache License v2.0 with Runtime Library Exception.
+  See LICENSE file in the project root for full license terms.
+}
+
+{
+  Blaise RTL — jumbo set operations.
+
+  A "jumbo" set is a `set of <enum>` whose element enum has more than 64
+  members (up to the 256 ceiling).  It cannot fit in a single CPU register,
+  so it is represented as an inline byte-array bitmap of NBytes bytes
+  (NBytes = ceil(BitCount/8), so at most 32).  Member ordinal k occupies
+  bit (k and 7) of byte (k shr 3):
+
+      byte index = k shr 3        (k div 8)
+      bit  mask  = 1 shl (k and 7)
+
+  Sets of 64 members or fewer keep the fast single-register representation
+  and never reach these helpers; the codegen backends emit calls here only
+  for the jumbo case.
+
+  All set pointers are the address of the first bitmap byte.  The binary
+  operators tolerate Dest aliasing A and/or B (e.g. S := S + T): the byte
+  loop runs strictly forward and reads both inputs for index i before
+  writing Dest[i], so full overlap is safe.
+}
+
+unit blaise_set;
+
+interface
+
+{ ------------------------------------------------------------------ }
+{ Jumbo set RTL public interface                                      }
+{ ------------------------------------------------------------------ }
+function  _SetIn(S: Pointer; Ord: Integer): Integer;          { 0 or 1 }
+procedure _SetInclude(S: Pointer; Ord: Integer);
+procedure _SetExclude(S: Pointer; Ord: Integer);
+procedure _SetUnion(Dest, A, B: Pointer; NBytes: Integer);    { Dest := A or B }
+procedure _SetInter(Dest, A, B: Pointer; NBytes: Integer);    { Dest := A and B }
+procedure _SetDiff(Dest, A, B: Pointer; NBytes: Integer);     { Dest := A and not B }
+function  _SetEqual(A, B: Pointer; NBytes: Integer): Integer;  { 1 if equal }
+procedure _SetCopy(Dest, Src: Pointer; NBytes: Integer);      { byte copy }
+
+implementation
+
+{ Read byte i of a bitmap. }
+function GetByte(S: Pointer; I: Integer): Integer;
+var
+  P: ^Byte;
+begin
+  P := S + I;
+  Result := P^;
+end;
+
+{ Write byte i of a bitmap. }
+procedure PutByte(S: Pointer; I, V: Integer);
+var
+  P: ^Byte;
+begin
+  P := S + I;
+  P^ := Byte(V);
+end;
+
+function _SetIn(S: Pointer; Ord: Integer): Integer;
+var
+  ByteIdx, BitMask, B: Integer;
+begin
+  if S = nil then
+    Exit(0);
+  ByteIdx := Ord shr 3;
+  BitMask := 1 shl (Ord and 7);
+  B := GetByte(S, ByteIdx);
+  if (B and BitMask) <> 0 then
+    Result := 1
+  else
+    Result := 0;
+end;
+
+procedure _SetInclude(S: Pointer; Ord: Integer);
+var
+  ByteIdx, BitMask, B: Integer;
+begin
+  ByteIdx := Ord shr 3;
+  BitMask := 1 shl (Ord and 7);
+  B := GetByte(S, ByteIdx);
+  PutByte(S, ByteIdx, B or BitMask);
+end;
+
+procedure _SetExclude(S: Pointer; Ord: Integer);
+var
+  ByteIdx, BitMask, B: Integer;
+begin
+  ByteIdx := Ord shr 3;
+  BitMask := 1 shl (Ord and 7);
+  B := GetByte(S, ByteIdx);
+  PutByte(S, ByteIdx, B and (not BitMask));
+end;
+
+procedure _SetUnion(Dest, A, B: Pointer; NBytes: Integer);
+var
+  I: Integer;
+begin
+  I := 0;
+  while I < NBytes do
+  begin
+    PutByte(Dest, I, GetByte(A, I) or GetByte(B, I));
+    Inc(I);
+  end;
+end;
+
+procedure _SetInter(Dest, A, B: Pointer; NBytes: Integer);
+var
+  I: Integer;
+begin
+  I := 0;
+  while I < NBytes do
+  begin
+    PutByte(Dest, I, GetByte(A, I) and GetByte(B, I));
+    Inc(I);
+  end;
+end;
+
+procedure _SetDiff(Dest, A, B: Pointer; NBytes: Integer);
+var
+  I: Integer;
+begin
+  I := 0;
+  while I < NBytes do
+  begin
+    PutByte(Dest, I, GetByte(A, I) and (not GetByte(B, I)));
+    Inc(I);
+  end;
+end;
+
+function _SetEqual(A, B: Pointer; NBytes: Integer): Integer;
+var
+  I: Integer;
+begin
+  I := 0;
+  while I < NBytes do
+  begin
+    if GetByte(A, I) <> GetByte(B, I) then
+      Exit(0);
+    Inc(I);
+  end;
+  Result := 1;
+end;
+
+procedure _SetCopy(Dest, Src: Pointer; NBytes: Integer);
+var
+  I: Integer;
+begin
+  I := 0;
+  while I < NBytes do
+  begin
+    PutByte(Dest, I, GetByte(Src, I));
+    Inc(I);
+  end;
+end;
+
+end.
diff --git a/tools/bif-coverage/bif-coverage.status b/tools/bif-coverage/bif-coverage.status
index 3047e80..b445f9a 100644
--- a/tools/bif-coverage/bif-coverage.status
+++ b/tools/bif-coverage/bif-coverage.status
@@ -24,9 +24,9 @@ TStringSubscriptExpr.IndexExpr  serialise
 TArrayLiteralExpr.Elements  serialise
 TArrayLiteralExpr.IsConstArray  safe
 
-# TNilLiteral (uAST.pas:70)
+# TNilLiteral (uAST.pas:74)
 
-# TIdentExpr (uAST.pas:79)
+# TIdentExpr (uAST.pas:83)
 TIdentExpr.Name  serialise
 TIdentExpr.ParamMode  safe
 TIdentExpr.IsConstant  safe
@@ -39,7 +39,7 @@ TIdentExpr.IsImplicitSelfMethod  safe
 TIdentExpr.IsMetaclassRef  safe
 TIdentExpr.ConstArraySymbol  safe
 
-# TFieldAccessExpr (uAST.pas:100)
+# TFieldAccessExpr (uAST.pas:104)
 TFieldAccessExpr.RecordName  serialise
 TFieldAccessExpr.FieldName  serialise
 TFieldAccessExpr.Base  serialise
@@ -64,29 +64,29 @@ TFieldAccessExpr.PropIndexExpr  serialise
 TFieldAccessExpr.IsCharAccess  safe
 TFieldAccessExpr.IsArrayAccess  safe
 
-# TIsExpr (uAST.pas:132)
+# TIsExpr (uAST.pas:136)
 TIsExpr.Obj  serialise
 TIsExpr.TypeName  serialise
 
-# TAsExpr (uAST.pas:140)
+# TAsExpr (uAST.pas:144)
 TAsExpr.Obj  serialise
 TAsExpr.TypeName  serialise
 
-# TSupportsExpr (uAST.pas:149)
+# TSupportsExpr (uAST.pas:153)
 TSupportsExpr.Obj  serialise
 TSupportsExpr.IntfTypeName  serialise
 TSupportsExpr.OutVarName  serialise
 TSupportsExpr.OutVarIsGlobal  safe
 
-# TBinaryExpr (uAST.pas:165)
+# TBinaryExpr (uAST.pas:169)
 TBinaryExpr.Op  serialise
 TBinaryExpr.Left  serialise
 TBinaryExpr.Right  serialise
 
-# TNotExpr (uAST.pas:173)
+# TNotExpr (uAST.pas:177)
 TNotExpr.Expr  serialise
 
-# TAssignment (uAST.pas:185)
+# TAssignment (uAST.pas:189)
 TAssignment.Name  serialise
 TAssignment.Expr  serialise
 TAssignment.IsVarParam  safe
@@ -95,23 +95,23 @@ TAssignment.IsThreadVar  safe
 TAssignment.IsWeakLhs  safe
 TAssignment.ImplicitSelfField  safe
 
-# TIfStmt (uAST.pas:201)
+# TIfStmt (uAST.pas:205)
 TIfStmt.Condition  serialise
 TIfStmt.ThenStmt  serialise
 TIfStmt.ElseStmt  serialise
 
-# TCompoundStmt (uAST.pas:209)
+# TCompoundStmt (uAST.pas:213)
 TCompoundStmt.Stmts  serialise
 
-# TWhileStmt (uAST.pas:216)
+# TWhileStmt (uAST.pas:220)
 TWhileStmt.Condition  serialise
 TWhileStmt.Body  serialise
 
-# TRepeatStmt (uAST.pas:223)
+# TRepeatStmt (uAST.pas:227)
 TRepeatStmt.Body  serialise
 TRepeatStmt.Condition  serialise
 
-# TForStmt (uAST.pas:230)
+# TForStmt (uAST.pas:234)
 TForStmt.VarName  serialise
 TForStmt.IsGlobal  safe
 TForStmt.StartExpr  serialise
@@ -119,7 +119,7 @@ TForStmt.EndExpr  serialise
 TForStmt.IsDownTo  serialise
 TForStmt.Body  serialise
 
-# TForInStmt (uAST.pas:241)
+# TForInStmt (uAST.pas:245)
 TForInStmt.VarName  serialise
 TForInStmt.VarIsGlobal  safe
 TForInStmt.CollExpr  serialise
@@ -137,35 +137,36 @@ TForInStmt.AdvVarName  safe
 TForInStmt.IsSetIter  safe
 TForInStmt.SetBitCount  safe
 TForInStmt.SetMaskVarName  safe
+TForInStmt.SetIsJumbo  safe
 
-# TTryFinallyStmt (uAST.pas:274)
+# TTryFinallyStmt (uAST.pas:282)
 TTryFinallyStmt.TryBody  serialise
 TTryFinallyStmt.FinallyBody  serialise
 
-# TTryExceptStmt (uAST.pas:291)
+# TTryExceptStmt (uAST.pas:299)
 TTryExceptStmt.TryBody  serialise
 TTryExceptStmt.Handlers  serialise
 TTryExceptStmt.ElseBody  serialise
 TTryExceptStmt.ExceptBody  serialise
 
-# TRaiseStmt (uAST.pas:304)
+# TRaiseStmt (uAST.pas:312)
 TRaiseStmt.Expr  serialise
 
-# TExitStmt (uAST.pas:315)
+# TExitStmt (uAST.pas:323)
 TExitStmt.Value  safe
 TExitStmt.ResultAssign  safe
 
-# TBreakStmt (uAST.pas:323)
+# TBreakStmt (uAST.pas:331)
 
-# TContinueStmt (uAST.pas:326)
+# TContinueStmt (uAST.pas:334)
 
-# TCaseStmt (uAST.pas:337)
+# TCaseStmt (uAST.pas:345)
 TCaseStmt.Selector  serialise
 TCaseStmt.Branches  serialise
 TCaseStmt.ElseStmt  serialise
 TCaseStmt.IsStringCase  safe
 
-# TFieldAssignment (uAST.pas:348)
+# TFieldAssignment (uAST.pas:356)
 TFieldAssignment.RecordName  serialise
 TFieldAssignment.FieldName  serialise
 TFieldAssignment.Expr  serialise
@@ -179,7 +180,7 @@ TFieldAssignment.PropIndexExpr  serialise
 TFieldAssignment.PropOwnerType  safe
 TFieldAssignment.IsElemWrite  safe
 
-# TStaticSubscriptAssign (uAST.pas:375)
+# TStaticSubscriptAssign (uAST.pas:383)
 TStaticSubscriptAssign.ArrayName  serialise
 TStaticSubscriptAssign.IndexExpr  serialise
 TStaticSubscriptAssign.ValueExpr  serialise
@@ -188,18 +189,18 @@ TStaticSubscriptAssign.IsGlobal  safe
 TStaticSubscriptAssign.IsVarParam  safe
 TStaticSubscriptAssign.IsImplicitSelf  safe
 
-# TPointerWriteStmt (uAST.pas:398)
+# TPointerWriteStmt (uAST.pas:406)
 TPointerWriteStmt.PtrExpr  serialise
 TPointerWriteStmt.ValExpr  serialise
 
-# TProcCall (uAST.pas:406)
+# TProcCall (uAST.pas:414)
 TProcCall.Name  serialise
 TProcCall.Args  serialise
 TProcCall.IsImplicitSelfMethod  safe
 TProcCall.IsIndirectCall  safe
 TProcCall.IndirectCallIsGlobal  safe
 
-# TFuncCallExpr (uAST.pas:419)
+# TFuncCallExpr (uAST.pas:427)
 TFuncCallExpr.Name  serialise
 TFuncCallExpr.Args  serialise
 TFuncCallExpr.IsImplicitSelfMethod  safe
@@ -209,18 +210,18 @@ TFuncCallExpr.IsBuiltinHasClassAttr  safe
 TFuncCallExpr.HasClassAttrClass  safe
 TFuncCallExpr.HasClassAttrAttr  safe
 
-# TIndirectFuncCallExpr (uAST.pas:445)
+# TIndirectFuncCallExpr (uAST.pas:453)
 TIndirectFuncCallExpr.CalleeExpr  serialise
 TIndirectFuncCallExpr.Args  serialise
 
-# TDerefExpr (uAST.pas:455)
+# TDerefExpr (uAST.pas:463)
 TDerefExpr.Expr  serialise
 
-# TAddrOfExpr (uAST.pas:462)
+# TAddrOfExpr (uAST.pas:470)
 TAddrOfExpr.Expr  serialise
 TAddrOfExpr.ResolvedFreeRoutine  safe
 
-# TMethodCallStmt (uAST.pas:474)
+# TMethodCallStmt (uAST.pas:482)
 TMethodCallStmt.ObjectName  serialise
 TMethodCallStmt.Name  serialise
 TMethodCallStmt.Args  serialise
@@ -231,11 +232,11 @@ TMethodCallStmt.IsVarParam  safe
 TMethodCallStmt.IsBuiltinToString  safe
 TMethodCallStmt.IsProcFieldCall  safe
 
-# TInheritedCallStmt (uAST.pas:506)
+# TInheritedCallStmt (uAST.pas:514)
 TInheritedCallStmt.Name  serialise
 TInheritedCallStmt.Args  serialise
 
-# TMethodCallExpr (uAST.pas:696)
+# TMethodCallExpr (uAST.pas:789)
 TMethodCallExpr.ObjectName  serialise
 TMethodCallExpr.Name  serialise
 TMethodCallExpr.Args  serialise