diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 796f5dcad6e5e..092a2d48bfd3e 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -517,7 +517,7 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
 		return ret;
 	}
 
-	if (subflow->use_64bit_ack) {
+	if (READ_ONCE(msk->use_64bit_ack)) {
 		ack_size = TCPOLEN_MPTCP_DSS_ACK64;
 		opts->ext_copy.data_ack = READ_ONCE(msk->ack_seq);
 		opts->ext_copy.ack64 = 1;
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 551cb2afa10d7..fd0417b6c9b6a 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -212,6 +212,7 @@ struct mptcp_sock {
 	bool		fully_established;
 	bool		rcv_data_fin;
 	bool		snd_data_fin_enable;
+	bool		use_64bit_ack; /* Set when we received a 64-bit DSN */
 	spinlock_t	join_list_lock;
 	struct work_struct work;
 	struct sk_buff  *ooo_last_skb;
@@ -311,7 +312,6 @@ struct mptcp_subflow_context {
 		mpc_map : 1,
 		backup : 1,
 		rx_eof : 1,
-		use_64bit_ack : 1, /* Set when we received a 64-bit DSN */
 		can_ack : 1;	    /* only after processing the remote a key */
 	enum mptcp_data_avail data_avail;
 	u32	remote_nonce;
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index a69e7ee9d6cb4..ac4a1fe3550bd 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -782,12 +782,11 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 	if (!mpext->dsn64) {
 		map_seq = expand_seq(subflow->map_seq, subflow->map_data_len,
 				     mpext->data_seq);
-		subflow->use_64bit_ack = 0;
 		pr_debug("expanded seq=%llu", subflow->map_seq);
 	} else {
 		map_seq = mpext->data_seq;
-		subflow->use_64bit_ack = 1;
 	}
+	WRITE_ONCE(mptcp_sk(subflow->conn)->use_64bit_ack, !!mpext->dsn64);
 
 	if (subflow->map_valid) {
 		/* Allow replacing only with an identical map */