diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 036f857..1db6639 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5964,7 +5964,7 @@
 
 	req = tp->fastopen_rsk;
 	if (req != NULL) {
-		BUG_ON(sk->sk_state != TCP_SYN_RECV &&
+		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
 		    sk->sk_state != TCP_FIN_WAIT1);
 
 		if (tcp_check_req(sk, skb, req, NULL, true) == NULL)
@@ -6053,7 +6053,15 @@
 			 * ACK we have received, this would have acknowledged
 			 * our SYNACK so stop the SYNACK timer.
 			 */
-			if (acceptable && req != NULL) {
+			if (req != NULL) {
+				/* Return RST if ack_seq is invalid.
+				 * Note that RFC793 only says to generate a
+				 * DUPACK for it but for TCP Fast Open it seems
+				 * better to treat this case like TCP_SYN_RECV
+				 * above.
+				 */
+				if (!acceptable)
+					return 1;
 				/* We no longer need the request sock. */
 				reqsk_fastopen_remove(sk, req, false);
 				tcp_rearm_rto(sk);
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index fc04711..d47c1b4 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -347,8 +347,8 @@
 		return;
 	}
 	if (tp->fastopen_rsk) {
-		BUG_ON(sk->sk_state != TCP_SYN_RECV &&
-		    sk->sk_state != TCP_FIN_WAIT1);
+		WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
+			     sk->sk_state != TCP_FIN_WAIT1);
 		tcp_fastopen_synack_timer(sk);
 		/* Before we receive ACK to our SYN-ACK don't retransmit
 		 * anything else (e.g., data or FIN segments).