diff --git a/TestSuite/where21.pas b/TestSuite/where21.pas
new file mode 100644
index 000000000..c35ae6735
--- /dev/null
+++ b/TestSuite/where21.pas
@@ -0,0 +1,16 @@
+type
+  c1<T1> = class
+  where T1: IComparable<T1>;
+    
+    function f1<T2>(o: T2): integer;
+      where T2: T1;
+    begin
+      Result := {T1}(o).CompareTo({T1}(o));
+    end;
+    
+  end;
+  
+begin
+  var a := new c1<string>;
+  assert(a.f1('abc') = 0);
+end.
\ No newline at end of file