diff --git a/tmate-proxy.c b/tmate-proxy.c
index c8b4606b..7af94a78 100644
--- a/tmate-proxy.c
+++ b/tmate-proxy.c
@@ -196,6 +196,8 @@ void tmate_notify_client_join(__unused struct tmate_session *session,
 	if (!tmate_has_proxy())
 		return;
 
+	c->flags |= CLIENT_TMATE_NOTIFIED_JOIN;
+
 	pack(array, 5);
 	pack(int, TMATE_CTL_CLIENT_JOIN);
 	pack(int, c->id);
@@ -212,6 +214,11 @@ void tmate_notify_client_left(__unused struct tmate_session *session,
 	if (!tmate_has_proxy())
 		return;
 
+	if (!(c->flags & CLIENT_TMATE_NOTIFIED_JOIN))
+		return;
+
+	c->flags &= ~CLIENT_TMATE_NOTIFIED_JOIN;
+
 	pack(array, 2);
 	pack(int, TMATE_CTL_CLIENT_LEFT);
 	pack(int, c->id);
diff --git a/tmux.h b/tmux.h
index e4fc5824..01575cc9 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1280,6 +1280,9 @@ struct client {
 #define CLIENT_256COLOURS 0x20000
 #define CLIENT_IDENTIFIED 0x40000
 #define CLIENT_STATUSFORCE 0x80000
+#ifdef TMATE_SLAVE
+#define CLIENT_TMATE_NOTIFIED_JOIN 0x10000000
+#endif
 	int		 flags;
 	struct key_table *keytable;