https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81073
--- Comment #11 from Georg-Johann Lay <gjl at gcc dot gnu.org> --- ...oops, I missed the PROGMEM in PSTR definition. Should read: // A string in flash #define PSTR(str) \ (__extension__({ \ static const char __c[] PROGMEM = (str); \ &__c[0]; \ })) but still no error.