diff --git a/net/netfilter/nf_conntrack_h323_asn1.c b/net/netfilter/nf_conntrack_h323_asn1.c
index 7831aa1effc9..cf1bf2605c10 100644
--- a/net/netfilter/nf_conntrack_h323_asn1.c
+++ b/net/netfilter/nf_conntrack_h323_asn1.c
@@ -877,6 +877,7 @@ int DecodeQ931(unsigned char *buf, size_t sz, Q931 *q931)
 		if (sz < 1)
 			break;
 		len = *p++;
+		sz--;
 		if (sz < len)
 			break;
 		p += len;