diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index b884958..9a09ff3 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4735,11 +4735,11 @@ static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
 		if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
 			tcp_ofo_queue(sk);
 
-			/* RFC2581. 4.2. SHOULD send immediate ACK, when
+			/* RFC5681. 4.2. SHOULD send immediate ACK, when
 			 * gap in queue is filled.
 			 */
 			if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
-				inet_csk(sk)->icsk_ack.pingpong = 0;
+				inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
 		}
 
 		if (tp->rx_opt.num_sacks)