diff --git a/include/netinet/tcp.h b/include/netinet/tcp.h
index 282b29c5..3f890a13 100644
--- a/include/netinet/tcp.h
+++ b/include/netinet/tcp.h
@@ -172,6 +172,7 @@ enum
 # define TCPI_OPT_SACK		2
 # define TCPI_OPT_WSCALE	4
 # define TCPI_OPT_ECN		8
+# define TCPI_OPT_ECN_SEEN	16
 
 /* Values for tcpi_state.  */
 enum tcp_ca_state
diff --git a/misc/ss.c b/misc/ss.c
index af774d14..5ce40c04 100644
--- a/misc/ss.c
+++ b/misc/ss.c
@@ -1363,6 +1363,8 @@ static void tcp_show_info(const struct nlmsghdr *nlh, struct inet_diag_msg *r)
 				printf(" sack");
 			if (info->tcpi_options & TCPI_OPT_ECN)
 				printf(" ecn");
+			if (info->tcpi_options & TCPI_OPT_ECN_SEEN)
+				printf(" ecnseen");
 		}
 
 		if (tb[INET_DIAG_CONG])