https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106924
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- Oops, slightly further reduce to remove the ununsed print function: extern "C" int printf(const char*, ...); extern "C" void abort(); struct BaseA { virtual ~BaseA(){} }; struct BaseB { virtual ~BaseB(){} }; struct DerivedAB; struct FabForB { virtual BaseA* getPtr()=0; virtual ~FabForB(){} }; struct DerivedAB : BaseB, BaseA { struct ABFabNested : FabForB { virtual DerivedAB* getPtr(); }; }; DerivedAB d; DerivedAB* DerivedAB::ABFabNested::getPtr() { DerivedAB* p = &d; printf("TEST fab nested: addr %p base %p\n", p, (BaseA*)p); return p; } struct ABFab : FabForB { virtual DerivedAB* getPtr() { DerivedAB* p = &d; printf("TEST fab: addr %p base %p\n", p, (BaseA*)p); return p; } }; int main() { ABFab fab; DerivedAB::ABFabNested fabNested; BaseA* a1 = fab.getPtr(); BaseA* a2 = static_cast<FabForB&>(fab).getPtr(); printf("TEST addr %p %p\n", a1, a2); a1 = fabNested.getPtr(); a2 = static_cast<FabForB&>(fabNested).getPtr(); printf("TEST nested addr %p %p\n", a1, a2); if (a1 != a2) abort(); } This fails at least as far back as 4.1.0, I didn't test further.