--- arpwatch-2.1a15/arpwatch.c.bogon	2007-08-09 13:53:47.000000000 +0200

+++ arpwatch-2.1a15/arpwatch.c	2007-08-09 13:58:17.000000000 +0200

@@ -730,11 +730,12 @@ addnet(register const char *str)

 	/* XXX hack */

 	n = ntohl(inet_addr(tstr));

-	while ((n & 0xff000000) == 0) {

-		n <<= 8;

-		if (n == 0)

-			return (0);

-	}

+	if (n || width != 32)

+		while ((n & 0xff000000) == 0) {

+			n <<= 8;

+			if (n == 0)

+				return (0);

+		}

 	n = htonl(n);

 	if (width != 0) {