static void
mouse_class_update_xc(pTHX_ SV* const metaclass PERL_UNUSED_DECL, HV* const stash, AV* const xc) {
AV* const linearized_isa = mro_get_linear_isa(stash);
- I32 const len = AvFILLp(linearized_isa);
+ I32 const len = AvFILLp(linearized_isa) + 1;
I32 i;
U32 flags = 0x00;
AV* const attrall = newAV();