diff -ur linux-2.6.11/net/ipv4/netfilter/ip_conntrack_proto_tcp.c linux-2.6.11-csum/net/ipv4/netfilter/ip_conntrack_proto_tcp.c
--- linux-2.6.11/net/ipv4/netfilter/ip_conntrack_proto_tcp.c	2005-05-27 11:47:48 +01:00
+++ linux-2.6.11-csum/net/ipv4/netfilter/ip_conntrack_proto_tcp.c	2005-05-27 11:48:07 +01:00
@@ -803,6 +803,7 @@
 	 */
 	/* FIXME: Source route IP option packets --RR */
 	if (hooknum == NF_IP_PRE_ROUTING
+	    && skb->ip_summed != CHECKSUM_UNNECESSARY
 	    && csum_tcpudp_magic(iph->saddr, iph->daddr, tcplen, IPPROTO_TCP,
 			         skb->ip_summed == CHECKSUM_HW ? skb->csum
 			      	 : skb_checksum(skb, iph->ihl*4, tcplen, 0))) {
diff -ur linux-2.6.11/net/ipv4/netfilter/ip_conntrack_proto_udp.c linux-2.6.11-csum/net/ipv4/netfilter/ip_conntrack_proto_udp.c
--- linux-2.6.11/net/ipv4/netfilter/ip_conntrack_proto_udp.c	2005-05-27 11:47:48 +01:00
+++ linux-2.6.11-csum/net/ipv4/netfilter/ip_conntrack_proto_udp.c	2005-05-27 11:48:07 +01:00
@@ -120,6 +120,7 @@
 	 * and moreover root might send raw packets.
 	 * FIXME: Source route IP option packets --RR */
 	if (hooknum == NF_IP_PRE_ROUTING
+	    && skb->ip_summed != CHECKSUM_UNNECESSARY
 	    && csum_tcpudp_magic(iph->saddr, iph->daddr, udplen, IPPROTO_UDP,
 			         skb->ip_summed == CHECKSUM_HW ? skb->csum
 			      	 : skb_checksum(skb, iph->ihl*4, udplen, 0))) {