https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120049
--- Comment #4 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> --- Vincent was able to reduce this further. Two files, gtk_sup.f90 and test.f90. $ cat gtk_sup.f90 module gtk_sup use, intrinsic :: iso_c_binding end module gtk_sup $ cat test.f90 program tests_gtk_sup use gtk_sup type(c_ptr), target :: val ! If you comment the following line, it compiles and runs: print *, c_associated(val, c_loc(val)) end program tests_gtk_sup $ gfc -c gtk_sup.f90 $ ls gtk_sup.f90 gtk_sup.mod gtk_sup.o test.f90 $ gfc -c test.f90 f951: internal compiler error: gfc_typename(): Undefined type 0x694bce diagnostic_report_diagnostic(diagnostic_context*, diagnostic_info*) ../../trunk/gcc/diagnostic.h:1180 0x694bce gfc_report_diagnostic ../../trunk/gcc/fortran/error.cc:250 0x694bce gfc_internal_error(char const*, ...) ../../trunk/gcc/fortran/error.cc:834 0x6d5ecf gfc_typename(gfc_typespec*, bool) ../../trunk/gcc/fortran/misc.cc:218 0x66335a gfc_check_c_associated(gfc_expr*, gfc_expr*) ../../trunk/gcc/fortran/check.cc:5977 0x6aeb92 check_specific ../../trunk/gcc/fortran/intrinsic.cc:4971 0x6b7bb5 gfc_intrinsic_func_interface(gfc_expr*, int) ../../trunk/gcc/fortran/intrinsic.cc:5217 0x72626b resolve_unknown_f ... Anyone have any thoughts?