diff --git a/src/kernel/boot/makeflop.c b/src/kernel/boot/makeflop.c
index b216c999b9..3445d9cf17 100644
--- a/src/kernel/boot/makeflop.c
+++ b/src/kernel/boot/makeflop.c
@@ -34,7 +34,7 @@ main(int argc, char *argv[])
 	int padding = 0;
 	int infd;
 	int outfd;
-	char opt;
+	signed char opt;
 	int err;
 
 	char *progName = argv[0];