https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87521
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- The meaning of "user-declared" in C++03 is closer to "has a function body" than the meaning in C++11, where it includes defaulted definitions. A defaulted definition in C++11 is equivalent to an implicit (i.e. not user-declared) definition in C++03. So I would argue that your type is a POD for the purposes of layout, and GCC is correct. Consider: struct Base { unsigned x; short y; #if __cplusplus >= 201103L ~Base() = default; #endif }; struct Der : Base { short z; }; int i[] = { sizeof(Base), sizeof(Der) }; I would argue that the #if block should not affect the ABI of this type, i.e. it should be identical in C++03 and C++11, so it should be a "POD for the purposes of layout". Otherwise adding explicitly-defaulted special members (to conform to guidance like the Rule of Zero) causes ABI changes.