https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78001
--- Comment #5 from Markus Trippelsdorf <trippels at gcc dot gnu.org> --- Well, markus@x4 ~ % clang++ -c n.ii n.ii:6:24: error: member function 'm_fn1' not viable: 'this' argument has type 'const B', but function is not marked const void m_fn2() const { m_fn1(); } ^~~~~ n.ii:3:8: note: 'm_fn1' declared here void m_fn1(); ^ 1 error generated. is clear immediately.