X-Git-Url: https://git.distorted.org.uk/~mdw/sgt/puzzles/blobdiff_plain/06dca34c9c4fee65ebeffbaa3278651c8d717765..f6143b12f528deed07700fb32bd7996a2f5c5580:/singles.c

diff --git a/singles.c b/singles.c
index d8016ff..c20d0cf 100644
--- a/singles.c
+++ b/singles.c
@@ -324,7 +324,7 @@ static char n2c(int num) {
 }
 
 static int c2n(char c) {
-    if (isdigit(c))
+    if (isdigit((unsigned char)c))
         return (int)(c - '0');
     else if (c >= 'a' && c <= 'z')
         return (int)(c - 'a' + 10);