diff --git a/sys/netinet/tcp_syncache.c b/sys/netinet/tcp_syncache.c
index f0a8883b735..5a37a7ab3f6 100644
--- a/sys/netinet/tcp_syncache.c
+++ b/sys/netinet/tcp_syncache.c
@@ -970,7 +970,7 @@ syncache_add(struct in_conninfo *inc, struct tcpopt *to, struct tcphdr *th,
 
 	INP_INFO_WLOCK_ASSERT(&tcbinfo);
 	INP_LOCK_ASSERT(inp);			/* listen socket */
-	KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_ACK,
+	KASSERT((th->th_flags & (TH_RST|TH_ACK|TH_SYN)) == TH_SYN,
 	    ("%s: unexpected tcp flags", __func__));
 
 	/*