diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index f7263fe2a2e4..ee70f597a4de 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -27,7 +27,9 @@ struct mptcp_ext {
 	u32		subflow_seq;
 	u16		data_len;
 	__sum16		csum;
-	u8		use_map:1,
+
+	struct_group(flags,
+		u8	use_map:1,
 			dsn64:1,
 			data_fin:1,
 			use_ack:1,
@@ -35,9 +37,10 @@ struct mptcp_ext {
 			mpc_map:1,
 			frozen:1,
 			reset_transient:1;
-	u8		reset_reason:4,
+		u8	reset_reason:4,
 			csum_reqd:1,
 			infinite_map:1;
+	); /* end of flags group */
 };
 
 #define MPTCPOPT_HMAC_LEN	20
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index 51ca334678b4..f9f587203c35 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -572,6 +572,11 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
 	unsigned int ack_size;
 	bool ret = false;
 
+	/* Zero `use_ack` and `use_map` flags with one shot. */
+	BUILD_BUG_ON(sizeof_field(struct mptcp_ext, flags) != sizeof(u16));
+	BUILD_BUG_ON(!IS_ALIGNED(offsetof(struct mptcp_ext, flags),
+				 sizeof(u16)));
+	*(u16 *)&opts->ext_copy.flags = 0;
 	opts->csum_reqd = READ_ONCE(msk->csum_enabled);
 	mpext = skb ? mptcp_get_ext(skb) : NULL;
 
@@ -595,7 +600,6 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
 	/* passive sockets msk will set the 'can_ack' after accept(), even
 	 * if the first subflow may have the already the remote key handy
 	 */
-	opts->ext_copy.use_ack = 0;
 	if (!READ_ONCE(msk->can_ack)) {
 		*size = ALIGN(dss_size, 4);
 		return ret;