diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index ce0de02f5a3a..c2f4d7bd080c 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -374,10 +374,10 @@ static void mptcp_parse_option(const struct sk_buff *skb,
 			break;
 
 		ptr += 2;
-		mp_opt->rcvr_key = get_unaligned_be64(ptr);
+		mp_opt->fc_recv_key = get_unaligned_be64(ptr);
 		ptr += 8;
 		mp_opt->suboptions |= OPTION_MPTCP_FASTCLOSE;
-		pr_debug("MP_FASTCLOSE: recv_key=%llu\n", mp_opt->rcvr_key);
+		pr_debug("MP_FASTCLOSE: recv_key=%llu\n", mp_opt->fc_recv_key);
 		break;
 
 	case MPTCPOPT_RST:
@@ -1258,7 +1258,7 @@ bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
 
 	if (unlikely(mp_opt.suboptions != OPTION_MPTCP_DSS)) {
 		if ((mp_opt.suboptions & OPTION_MPTCP_FASTCLOSE) &&
-		    READ_ONCE(msk->local_key) == mp_opt.rcvr_key) {
+		    READ_ONCE(msk->local_key) == mp_opt.fc_recv_key) {
 			WRITE_ONCE(msk->rcv_fastclose, true);
 			mptcp_schedule_work((struct sock *)msk);
 			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPFASTCLOSERX);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 0384d6a023f9..29b03275a59e 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -145,13 +145,13 @@ static inline bool before64(__u64 seq1, __u64 seq2)
 #define after64(seq2, seq1)	before64(seq1, seq2)
 
 struct mptcp_options_received {
-	u64	sndr_key;
-	u64	rcvr_key;
-	u64	data_ack;
-	u64	data_seq;
-	u32	subflow_seq;
-	u16	data_len;
-	__sum16	csum;
+	struct { /* DSS, also used by MP_CAPABLE with data */
+		u64	data_ack;
+		u64	data_seq;
+		u32	subflow_seq;
+		u16	data_len;
+		__sum16	csum;
+	};
 	struct_group(status,
 		u16 suboptions;
 		u16 use_map:1,
@@ -167,15 +167,29 @@ struct mptcp_options_received {
 		    deny_join_id0:1,
 		    __unused:2;
 	);
-	u8	join_id;
-	u32	token;
-	u32	nonce;
-	u64	thmac;
-	u8	hmac[MPTCPOPT_HMAC_LEN];
-	struct mptcp_addr_info addr;
 	struct mptcp_rm_list rm_list;
-	u64	ahmac;
-	u64	fail_seq;
+	/* Options below are mutually exclusive, see mptcp_parse_option() */
+	union {
+		struct { /* MP_CAPABLE */
+			u64	sndr_key;
+			u64	rcvr_key;
+		};
+		struct { /* MP_JOIN */
+			u32	nonce;
+			u8	join_id;
+			union {
+				u32	token;			 /* SYN */
+				u64	thmac;			 /* SYN + ACK */
+				u8	hmac[MPTCPOPT_HMAC_LEN]; /* ACK */
+			};
+		};
+		struct { /* ADD_ADDR */
+			struct mptcp_addr_info addr;
+			u64	ahmac;
+		};
+		u64	fail_seq;	/* MP_FAIL */
+		u64	fc_recv_key;	/* MP_FASTCLOSE */
+	};
 };
 
 static inline __be32 mptcp_option(u8 subopt, u8 len, u8 nib, u8 field)
@@ -593,7 +607,6 @@ struct mptcp_subflow_context {
 	bool	fully_established;  /* path validated */
 	u32	lent_mem_frag;
 	u32	remote_nonce;
-	u64	thmac;
 	u32	local_nonce;
 	u32	remote_token;
 	union {
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index f0a6725d2c37..14aa82647c3d 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -408,20 +408,21 @@ static struct dst_entry *subflow_v6_route_req(const struct sock *sk,
 #endif
 
 /* validate received truncated hmac and create hmac for third ACK */
-static bool subflow_thmac_valid(struct mptcp_subflow_context *subflow)
+static bool subflow_thmac_valid(struct mptcp_subflow_context *subflow,
+				u64 thmac)
 {
 	u8 hmac[SHA256_DIGEST_SIZE];
-	u64 thmac;
+	u64 expected_thmac;
 
 	subflow_generate_hmac(subflow->remote_key, subflow->local_key,
 			      subflow->remote_nonce, subflow->local_nonce,
 			      hmac);
 
-	thmac = get_unaligned_be64(hmac);
-	pr_debug("subflow=%p, token=%u, thmac=%llu, subflow->thmac=%llu\n",
-		 subflow, subflow->token, thmac, subflow->thmac);
+	expected_thmac = get_unaligned_be64(hmac);
+	pr_debug("subflow=%p, token=%u, expected_thmac=%llu, thmac=%llu\n",
+		 subflow, subflow->token, expected_thmac, thmac);
 
-	return thmac == subflow->thmac;
+	return expected_thmac == thmac;
 }
 
 void mptcp_subflow_reset(struct sock *ssk)
@@ -575,14 +576,13 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 		}
 
 		subflow->backup = mp_opt.backup;
-		subflow->thmac = mp_opt.thmac;
 		subflow->remote_nonce = mp_opt.nonce;
 		WRITE_ONCE(subflow->remote_id, mp_opt.join_id);
 		pr_debug("subflow=%p, thmac=%llu, remote_nonce=%u backup=%d\n",
-			 subflow, subflow->thmac, subflow->remote_nonce,
+			 subflow, mp_opt.thmac, subflow->remote_nonce,
 			 subflow->backup);
 
-		if (!subflow_thmac_valid(subflow)) {
+		if (!subflow_thmac_valid(subflow, mp_opt.thmac)) {
 			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_JOINSYNACKMAC);
 			subflow->reset_reason = MPTCP_RST_EMPTCP;
 			goto do_reset;