Avoid undefined behavior when char is signed. diff -ur xpdfopen-0.86.orig/sendx.c xpdfopen-0.86/sendx.c --- xpdfopen-0.86.orig/sendx.c 2012-01-28 01:39:39.000000000 +0100 +++ xpdfopen-0.86/sendx.c 2014-06-18 08:13:50.000000000 +0200 @@ -229,7 +229,7 @@ */ if (ks < 256) { - event.state = isupper((char)ks); + event.state = isupper((unsigned char)ks); switch (ks) { case 0x08: