diff --git a/changelog.d/6816.misc b/changelog.d/6816.misc
new file mode 100644
index 0000000000..a77ba1d7a5
--- /dev/null
+++ b/changelog.d/6816.misc
@@ -0,0 +1 @@
+Add background update to clean out left rooms from current state.
diff --git a/synapse/storage/data_stores/main/state.py b/synapse/storage/data_stores/main/state.py
index 9b6f68e777..4167f83c9b 100644
--- a/synapse/storage/data_stores/main/state.py
+++ b/synapse/storage/data_stores/main/state.py
@@ -365,6 +365,8 @@ class MainStateBackgroundUpdateStore(RoomMemberWorkerStore):
 
             left_rooms = set(room_ids) - joined_room_ids
 
+            logger.info("Deleting current state left rooms: %r", left_rooms)
+
             # First we get all users that we still think were joined to the
             # room. This is so that we can mark those device lists as
             # potentially stale, since there may have been a period where the