Don't tickle an unreasonable but standard C lib limitation, thank you Vin! src/ChangeLog addition: 2015-03-17 Aidan Kehoe <kehoea@parhasard.net> * data.c (fill_ichar_array): Be a bit more careful never to supply the C library's isupper() with a value outside of that range specified by the C standard. Thank you Vin Shelton for reporting the Linux segmentation violation this provokes, and happy St. Patrick's Day to everyone reading the XEmacs lists!