diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index bef9f04c22ba..b6771f9eb9d4 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1115,7 +1115,7 @@ static int tcp_is_sackblock_valid(struct tcp_sock *tp, int is_dsack,
 		return 0;
 
 	/* ...Then it's D-SACK, and must reside below snd_una completely */
-	if (!after(end_seq, tp->snd_una))
+	if (after(end_seq, tp->snd_una))
 		return 0;
 
 	if (!before(start_seq, tp->undo_marker))