1 files changed, 8 insertions, 1 deletions
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 907940e19e..28097664b4 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -824,7 +824,14 @@ class FederationServer(FederationBase):
                 context, self._room_prejoin_state_types
             )
         )
-        return {"knock_state_events": stripped_room_state}
+        return {
+            "knock_room_state": stripped_room_state,
+            # Since v1.37, Synapse incorrectly used "knock_state_events" for this field.
+            # Thus, we also populate a 'knock_state_events' with the same content to
+            # support old instances.
+            # See https://github.com/matrix-org/synapse/issues/14088.
+            "knock_state_events": stripped_room_state,
+        }
 
     async def _on_send_membership_event(
         self, origin: str, content: JsonDict, membership_type: str, room_id: str