1 files changed, 1 insertions, 1 deletions
diff --git a/muttlib.c b/muttlib.c
index 7994c95d..9b75b834 100644
--- a/muttlib.c
+++ b/muttlib.c
@@ -521,7 +521,7 @@ char *mutt_gecos_name (char *dest, size_t destlen, struct passwd *pw)
       memmove (&dest[idx + pwnl], &dest[idx + 1],
 	       MAX(destlen - idx - pwnl - 1, 0));
       memcpy (&dest[idx], pw->pw_name, MIN(destlen - idx - 1, pwnl));
-      dest[idx] = toupper (dest[idx]);
+      dest[idx] = toupper ((unsigned char) dest[idx]);
     }
   }