https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84717
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to stiefschmied from comment #0) > I think this is a compiler bug? The example code is attached. No. Compile with -Wpedantic and you see why it's accepted: 84717.c:3:21: warning: suffix for double constant is a GCC extension static double aem = 7.29735d-3; ^~~~~~~~ 84717.c:6:1: error: unknown type name ‘Int’; did you mean ‘int’? Int main() { ^~~ int Or use -Wpedantic-errors to reject it. I think the suffix is to distinguish 1.0d from 1.0f or 1.0l but I can't find any documentation on it.