{ %fail } program test; {$MODE DELPHI} type XBool = LongBool; XInt = Int64; XResult = type XInt; ITest = interface(IInterface) function Foobar: XResult; end; TTest = class(TInterfacedObject, ITest) function Foobar: XBool; end; function TTest.Foobar: LongBool; begin Result := True; end; begin end.