diff --git a/include/net/tcp.h b/include/net/tcp.h
index f357bef..702aefc 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -356,6 +356,7 @@
 #define	TCP_ECN_OK		1
 #define	TCP_ECN_QUEUE_CWR	2
 #define	TCP_ECN_DEMAND_CWR	4
+#define	TCP_ECN_SEEN		8
 
 static __inline__ void
 TCP_ECN_create_request(struct request_sock *req, struct tcphdr *th)