diff --git a/changelog.d/13365.bugfix b/changelog.d/13365.bugfix
new file mode 100644
index 000000000000..b915c3158cd4
--- /dev/null
+++ b/changelog.d/13365.bugfix
@@ -0,0 +1 @@
+Fix a bug introduced in Synapse v1.41.0 where the `/hierarchy` API returned non-standard information (a `room_id` field under each entry in `children_state`).
diff --git a/synapse/handlers/room_summary.py b/synapse/handlers/room_summary.py
index 13098f56ed26..85811b5bde83 100644
--- a/synapse/handlers/room_summary.py
+++ b/synapse/handlers/room_summary.py
@@ -452,7 +452,6 @@ async def _summarize_local_room(
                 "type": e.type,
                 "state_key": e.state_key,
                 "content": e.content,
-                "room_id": e.room_id,
                 "sender": e.sender,
                 "origin_server_ts": e.origin_server_ts,
             }