diff -ur v2.4.32/linux/net/ipv4/netfilter/ip_nat_core.c linux/net/ipv4/netfilter/ip_nat_core.c
--- v2.4.32/linux/net/ipv4/netfilter/ip_nat_core.c	2005-04-05 09:57:20.000000000 +0300
+++ linux/net/ipv4/netfilter/ip_nat_core.c	2005-12-10 15:38:12.044972384 +0200
@@ -626,7 +626,7 @@
 	}
 
 	/* If there's a helper, assign it; based on new tuple. */
-	if (!conntrack->master)
+	if (!conntrack->master && info->num_manips)
 		info->helper = LIST_FIND(&helpers, helper_cmp, struct ip_nat_helper *,
 					 &reply);
 
@@ -754,7 +754,7 @@
 	    struct sk_buff **pskb)
 {
 	unsigned int i;
-	struct ip_nat_helper *helper;
+	struct ip_nat_helper *helper = NULL;
 	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 	int is_tcp = (*pskb)->nh.iph->protocol == IPPROTO_TCP;
 
@@ -775,6 +775,7 @@
 			*pskb = nskb;
 		}
 
+		helper = info->helper;
 		if (info->manips[i].direction == dir
 		    && info->manips[i].hooknum == hooknum) {
 			DEBUGP("Mangling %p: %s to %u.%u.%u.%u %u\n",
@@ -791,7 +792,6 @@
 				  &(*pskb)->nfcache);
 		}
 	}
-	helper = info->helper;
 	READ_UNLOCK(&ip_nat_lock);
 
 	if (helper) {