this is a prvalue, so decltype(this) should always be plain X* (or X cv* / cv X*). The addition of const& seems to be a bug in GCC (tested with g++ 4.8.1), which happens only for a class template (not for a “plain” class) and only inside the trailing return type (not inside the body of the member function): demo. This seems to be fixed in GCC 4.9 (experimental), you can test here.