diff --git a/sys/netinet/in.c b/sys/netinet/in.c
--- a/sys/netinet/in.c
+++ b/sys/netinet/in.c
@@ -276,7 +276,8 @@
 {
 	u_long i = ntohl(in.s_addr);
 
-	if (IN_MULTICAST(i) || IN_LINKLOCAL(i) || IN_LOOPBACK(i))
+	if (IN_MULTICAST(i) || IN_LINKLOCAL(i) || IN_LOOPBACK(i) ||
+	    in_nullhost(in))
 		return (0);
 	if (IN_EXPERIMENTAL(i) && !V_ip_allow_net240)
 		return (0);
diff --git a/sys/netinet/ip_icmp.c b/sys/netinet/ip_icmp.c
--- a/sys/netinet/ip_icmp.c
+++ b/sys/netinet/ip_icmp.c
@@ -783,10 +783,11 @@
 
 	if (IN_MULTICAST(ntohl(ip->ip_src.s_addr)) ||
 	    (IN_EXPERIMENTAL(ntohl(ip->ip_src.s_addr)) && !V_ip_allow_net240) ||
-	    (IN_ZERONET(ntohl(ip->ip_src.s_addr)) && !V_ip_allow_net0) ) {
+	    (IN_ZERONET(ntohl(ip->ip_src.s_addr)) && !V_ip_allow_net0) ||
+	    in_nullhost(ip->ip_src) ) {
 		m_freem(m);	/* Bad return address */
 		ICMPSTAT_INC(icps_badaddr);
-		goto done;	/* Ip_output() will check for broadcast */
+		goto done;	/* ip_output() will check for broadcast */
 	}
 
 	t = ip->ip_dst;