diff --git a/libxtables/xtables.c b/libxtables/xtables.c
index ef5bc07..8437baf 100644
--- a/libxtables/xtables.c
+++ b/libxtables/xtables.c
@@ -1243,7 +1243,7 @@
 	uint32_t cidr;
 
 	cidr = xtables_ipmask_to_cidr(mask);
-	if (cidr < 0) {
+	if (cidr == (unsigned int)-1) {
 		/* mask was not a decent combination of 1's and 0's */
 		sprintf(buf, "/%s", xtables_ipaddr_to_numeric(mask));
 		return buf;