diff --git a/net/ipv4/netfilter/ipt_SYNPROXY.c b/net/ipv4/netfilter/ipt_SYNPROXY.c
index 01cffeaa0085ede5bb802999fc1f29c9e6ec4b7f..f13bd91d9a56774f58dcf14de892b2bedd855cc5 100644
--- a/net/ipv4/netfilter/ipt_SYNPROXY.c
+++ b/net/ipv4/netfilter/ipt_SYNPROXY.c
@@ -244,6 +244,7 @@ synproxy_recv_client_ack(const struct synproxy_net *snet,
 
 	this_cpu_inc(snet->stats->cookie_valid);
 	opts->mss = mss;
+	opts->options |= XT_SYNPROXY_OPT_MSS;
 
 	if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
 		synproxy_check_timestamp_cookie(opts);
diff --git a/net/ipv6/netfilter/ip6t_SYNPROXY.c b/net/ipv6/netfilter/ip6t_SYNPROXY.c
index bf9f612c1bc24eb9eb0b26fbf7d0a62f74932735..f78f41aca8e90967a026a145f938746ce317cf10 100644
--- a/net/ipv6/netfilter/ip6t_SYNPROXY.c
+++ b/net/ipv6/netfilter/ip6t_SYNPROXY.c
@@ -259,6 +259,7 @@ synproxy_recv_client_ack(const struct synproxy_net *snet,
 
 	this_cpu_inc(snet->stats->cookie_valid);
 	opts->mss = mss;
+	opts->options |= XT_SYNPROXY_OPT_MSS;
 
 	if (opts->options & XT_SYNPROXY_OPT_TIMESTAMP)
 		synproxy_check_timestamp_cookie(opts);