diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 09b19aa2f205..6628d8d74203 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -877,6 +877,9 @@ static void __mptcp_wmem_reserve(struct sock *sk, int size)
 	struct mptcp_sock *msk = mptcp_sk(sk);
 
 	WARN_ON_ONCE(msk->wmem_reserved);
+	if (WARN_ON_ONCE(amount < 0))
+		amount = 0;
+
 	if (amount <= sk->sk_forward_alloc)
 		goto reserve;
 
@@ -1587,7 +1590,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	if (msg->msg_flags & ~(MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL))
 		return -EOPNOTSUPP;
 
-	mptcp_lock_sock(sk, __mptcp_wmem_reserve(sk, len));
+	mptcp_lock_sock(sk, __mptcp_wmem_reserve(sk, min_t(size_t, 1 << 20, len)));
 
 	timeo = sock_sndtimeo(sk, msg->msg_flags & MSG_DONTWAIT);