diff --git a/net/ipv4/netfilter/nf_nat_sip.c b/net/ipv4/netfilter/nf_nat_sip.c
index bb71caa..6dbcdb1 100644
--- a/net/ipv4/netfilter/nf_nat_sip.c
+++ b/net/ipv4/netfilter/nf_nat_sip.c
@@ -148,7 +148,7 @@ static unsigned int ip_nat_sip(struct sk_buff *skb, unsigned int dataoff,
 	if (ct_sip_parse_header_uri(ct, *dptr, NULL, *datalen,
 				    hdr, NULL, &matchoff, &matchlen,
 				    &addr, &port) > 0) {
-		unsigned int matchend, poff, plen, buflen, n;
+		unsigned int olen, matchend, poff, plen, buflen, n;
 		char buffer[sizeof("nnn.nnn.nnn.nnn:nnnnn")];
 
 		/* We're only interested in headers related to this
@@ -163,11 +163,12 @@ static unsigned int ip_nat_sip(struct sk_buff *skb, unsigned int dataoff,
 				goto next;
 		}
 
+		olen = *datalen;
 		if (!map_addr(skb, dataoff, dptr, datalen, matchoff, matchlen,
 			      &addr, port))
 			return NF_DROP;
 
-		matchend = matchoff + matchlen;
+		matchend = matchoff + matchlen + *datalen - olen;
 
 		/* The maddr= parameter (RFC 2361) specifies where to send
 		 * the reply. */