Although this specific example doesn't reproduce the problem in a small project, this caused the problem in a larger project. The function was defined as follows: interface function CompareItemEqualStatus(const Value1: TSomeEnumeratedType; const Value2: TSomeEnumeratedType): Integer; implementation function CompareItemEqualStatus(const Value1: TSomeEnumeratedType; const Value2: TSomeEnumeratedType): Integer; overload; begin ... end;