diff --git a/synapse/replication/http/membership.py b/synapse/replication/http/membership.py
index 9f2a2e9fe490..08095fdf7d2c 100644
--- a/synapse/replication/http/membership.py
+++ b/synapse/replication/http/membership.py
@@ -181,9 +181,9 @@ async def _serialize_payload(room_id, user_id, change):
         Args:
             room_id (str)
             user_id (str)
-            change (str): Either "joined" or "left"
+            change (str): "left"
         """
-        assert change in ("joined", "left")
+        assert change == "left"
 
         return {}