diff --git a/apps/rand.c b/apps/rand.c
index cfbba30755869ac33e78558191cf18d65276f81d..fa9bc023f4059cfd7468f8847487abc79ae05713 100644
--- a/apps/rand.c
+++ b/apps/rand.c
@@ -62,7 +62,7 @@ int MAIN(int argc, char **argv)
 			else
 				badopt = 1;
 			}
-		else if (isdigit(argv[i][0]))
+		else if (isdigit((unsigned char)argv[i][0]))
 			{
 			if (num < 0)
 				{