diff --git a/changelog.d/14917.misc b/changelog.d/14917.misc
index 8a248495b2..4d1dd2639a 100644
--- a/changelog.d/14917.misc
+++ b/changelog.d/14917.misc
@@ -1 +1 @@
-Improve performance of looking up partial-state status.
+Faster joins: Improve performance of looking up partial-state status of rooms.
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 32f4ed228a..6095513277 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -1408,7 +1408,7 @@ class SyncHandler:
             forced_newly_joined_room_ids.update(
                 room_id
                 for room_id, is_partial_state in results.items()
-                if is_partial_state
+                if not is_partial_state
             )
 
         # Now we have our list of joined room IDs, exclude as configured and freeze