diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index 46c9e2ccdf02..7d83f90f203f 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -45,6 +45,7 @@ struct inet_connection_sock_af_ops {
 				      struct dst_entry *dst);
 	struct inet_peer *(*get_peer)(struct sock *sk, bool *release_it);
 	u16	    net_header_len;
+	u16	    net_frag_header_len;
 	u16	    sockaddr_len;
 	int	    (*setsockopt)(struct sock *sk, int level, int optname, 
 				  char __user *optval, unsigned int optlen);
diff --git a/include/net/tcp.h b/include/net/tcp.h
index fc880e92164a..0fb84de6da36 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -544,8 +544,8 @@ extern int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
 
 extern void tcp_initialize_rcv_mss(struct sock *sk);
 
-extern int tcp_mtu_to_mss(const struct sock *sk, int pmtu);
-extern int tcp_mss_to_mtu(const struct sock *sk, int mss);
+extern int tcp_mtu_to_mss(struct sock *sk, int pmtu);
+extern int tcp_mss_to_mtu(struct sock *sk, int mss);
 extern void tcp_mtup_init(struct sock *sk);
 extern void tcp_valid_rtt_meas(struct sock *sk, u32 seq_rtt);
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 7b7cf3811348..834e89fc541b 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1150,7 +1150,7 @@ int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
 }
 
 /* Calculate MSS. Not accounting for SACKs here.  */
-int tcp_mtu_to_mss(const struct sock *sk, int pmtu)
+int tcp_mtu_to_mss(struct sock *sk, int pmtu)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	const struct inet_connection_sock *icsk = inet_csk(sk);
@@ -1161,6 +1161,14 @@ int tcp_mtu_to_mss(const struct sock *sk, int pmtu)
 	 */
 	mss_now = pmtu - icsk->icsk_af_ops->net_header_len - sizeof(struct tcphdr);
 
+	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
+	if (icsk->icsk_af_ops->net_frag_header_len) {
+		const struct dst_entry *dst = __sk_dst_get(sk);
+
+		if (dst && dst_allfrag(dst))
+			mss_now -= icsk->icsk_af_ops->net_frag_header_len;
+	}
+
 	/* Clamp it (mss_clamp does not include tcp options) */
 	if (mss_now > tp->rx_opt.mss_clamp)
 		mss_now = tp->rx_opt.mss_clamp;
@@ -1179,7 +1187,7 @@ int tcp_mtu_to_mss(const struct sock *sk, int pmtu)
 }
 
 /* Inverse of above */
-int tcp_mss_to_mtu(const struct sock *sk, int mss)
+int tcp_mss_to_mtu(struct sock *sk, int mss)
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 	const struct inet_connection_sock *icsk = inet_csk(sk);
@@ -1190,6 +1198,13 @@ int tcp_mss_to_mtu(const struct sock *sk, int mss)
 	      icsk->icsk_ext_hdr_len +
 	      icsk->icsk_af_ops->net_header_len;
 
+	/* IPv6 adds a frag_hdr in case RTAX_FEATURE_ALLFRAG is set */
+	if (icsk->icsk_af_ops->net_frag_header_len) {
+		const struct dst_entry *dst = __sk_dst_get(sk);
+
+		if (dst && dst_allfrag(dst))
+			mtu += icsk->icsk_af_ops->net_frag_header_len;
+	}
 	return mtu;
 }
 
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index cdbf292ad208..57b210969834 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1778,6 +1778,7 @@ static const struct inet_connection_sock_af_ops ipv6_specific = {
 	.syn_recv_sock	   = tcp_v6_syn_recv_sock,
 	.get_peer	   = tcp_v6_get_peer,
 	.net_header_len	   = sizeof(struct ipv6hdr),
+	.net_frag_header_len = sizeof(struct frag_hdr),
 	.setsockopt	   = ipv6_setsockopt,
 	.getsockopt	   = ipv6_getsockopt,
 	.addr2sockaddr	   = inet6_csk_addr2sockaddr,