diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
index d17b46d1303..16871d7d828 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -2256,6 +2256,8 @@ tcp_send_challenge_ack(struct tcpcb *tp, struct tcphdr *th, struct mbuf *m)
 		tcp_respond(tp, mtod(m, void *), th, m, tp->rcv_nxt,
 		    tp->snd_nxt, TH_ACK);
 		tp->last_ack_sent = tp->rcv_nxt;
+	} else {
+		m_freem(m);
 	}
 }