diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 3bcd30a..f9dcb29 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -246,8 +246,15 @@ static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
 
 static void tcp_ecn_accept_cwr(struct tcp_sock *tp, const struct sk_buff *skb)
 {
-	if (tcp_hdr(skb)->cwr)
+	if (tcp_hdr(skb)->cwr) {
 		tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
+
+		/* If the sender is telling us it has entered CWR, then its
+		 * cwnd may be very low (even just 1 packet), so we should ACK
+		 * immediately.
+		 */
+		tcp_enter_quickack_mode((struct sock *)tp, 2);
+	}
 }
 
 static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)