The following example doesn't compile because of the ambiguous overloads of `__invoke`: #include <type_traits> struct wat { wat& operator*() { return *this; } void foo(); }; int main(){ using type = std::result_of<decltype(&wat::foo)(wat)>::type; } The standard (indirectly) states in 20.8.1 [func.require] p1 that the second bullet only applies if the first bullet does not, through the restrictions on the type of `t1`. The same problem appears with member data pointers (bullets 3 and 4). One possible resolution is to remove the respective overloads from overload resolution depending on whether the type of `t1` is a type derived from the class of the member pointer.
Thanks for narrowing this bug report down to such a concise test case. Fix committed revision 181377.