--- sys/netinet/ip_icmp.c.orig	Wed Apr 21 11:17:44 2004
+++ sys/netinet/ip_icmp.c	Fri Apr 23 17:30:01 2004
@@ -168,6 +168,11 @@
 	if (icmp_ratelimit(&oip->ip_src, type, code))
 		goto freeit;	/* XXX stat */
 
+	if (oiplen > sizeof(struct ip)) {
+		oip->ip_sum = 0;
+		oip->ip_sum = in_cksum(n, oiplen);
+	}
+
 	/*
 	 * Now, formulate icmp message
 	 */