diff --git a/SyntaxTree/tree/Tree.cs b/SyntaxTree/tree/Tree.cs
index 3119c44c8..fba02008c 100644
--- a/SyntaxTree/tree/Tree.cs
+++ b/SyntaxTree/tree/Tree.cs
@@ -46374,6 +46374,7 @@ namespace PascalABCCompiler.SyntaxTree
 		{
 			yield_unknown_ident copy = new yield_unknown_ident();
 			copy.Parent = this.Parent;
+			copy.UnknownID = this.UnknownID;
 			if (source_context != null)
 				copy.source_context = new SourceContext(source_context);
 			if (attributes != null)
diff --git a/TestSuite/yield6.pas b/TestSuite/yield6.pas
new file mode 100644
index 000000000..675aa00c4
--- /dev/null
+++ b/TestSuite/yield6.pas
@@ -0,0 +1,17 @@
+type
+  t1 = class
+    
+    function f1: sequence of byte;
+    begin
+      
+      var p: function: sequence of integer := ()->
+      |(1,2)|.Select(\(a,b)->3);
+      yield p().ToArray()[0];
+    end;
+    
+  end;
+  
+begin 
+  var o := new t1;
+  assert(o.f1.ToArray[0] = 3);
+end.
\ No newline at end of file