diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 6c1f96f6ae39..0087a598a383 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -906,6 +906,13 @@ static bool __mptcp_finish_join(struct mptcp_sock *msk, struct sock *ssk)
 	if (sk->sk_state != TCP_ESTABLISHED)
 		return false;
 
+	/* The caller possibly is not holding the msk socket lock, but
+	 * in the fallback case only the current subflow is touching
+	 * the OoO queue.
+	 */
+	if (!RB_EMPTY_ROOT(&msk->out_of_order_queue))
+		return false;
+
 	spin_lock_bh(&msk->fallback_lock);
 	if (!msk->allow_subflows) {
 		spin_unlock_bh(&msk->fallback_lock);