diff --git a/tc/m_tunnel_key.c b/tc/m_tunnel_key.c
index 58a3042a..3ceec1cb 100644
--- a/tc/m_tunnel_key.c
+++ b/tc/m_tunnel_key.c
@@ -22,7 +22,7 @@
 static void explain(void)
 {
 	fprintf(stderr, "Usage: tunnel_key unset\n");
-	fprintf(stderr, "       tunnel_key set id TUNNELID src_ip IP dst_ip IP\n");
+	fprintf(stderr, "       tunnel_key set id TUNNELID src_ip IP dst_ip IP dst_port UDP_PORT\n");
 }
 
 static void usage(void)