diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
index bb9fc852e973ad005485cf478eb5605e8ca44664..4a0496aa32d553dc41534a3ff90cbe5126d2a5f6 100644
--- a/include/net/netfilter/nf_conntrack.h
+++ b/include/net/netfilter/nf_conntrack.h
@@ -65,14 +65,7 @@ union nf_conntrack_help {
 #include <linux/timer.h>
 
 #ifdef CONFIG_NETFILTER_DEBUG
-#define NF_CT_ASSERT(x)							\
-do {									\
-	if (!(x))							\
-		/* Wooah!  I'm tripping my conntrack in a frenzy of	\
-		   netplay... */					\
-		printk("NF_CT_ASSERT: %s:%i(%s)\n",			\
-		       __FILE__, __LINE__, __FUNCTION__);		\
-} while(0)
+#define NF_CT_ASSERT(x)		WARN_ON(!(x))
 #else
 #define NF_CT_ASSERT(x)
 #endif
diff --git a/net/netfilter/nf_conntrack_extend.c b/net/netfilter/nf_conntrack_extend.c
index 2bd9963b5b3ea4cf26d4abde679a72e8b28421a7..bcc19fa4ed1e07ab4277f7c02c933235cd0dc261 100644
--- a/net/netfilter/nf_conntrack_extend.c
+++ b/net/netfilter/nf_conntrack_extend.c
@@ -71,6 +71,9 @@ void *__nf_ct_ext_add(struct nf_conn *ct, enum nf_ct_ext_id id, gfp_t gfp)
 	int i, newlen, newoff;
 	struct nf_ct_ext_type *t;
 
+	/* Conntrack must not be confirmed to avoid races on reallocation. */
+	NF_CT_ASSERT(!nf_ct_is_confirmed(ct));
+
 	if (!ct->ext)
 		return nf_ct_ext_create(&ct->ext, id, gfp);