diff --git a/changelog.d/17208.misc b/changelog.d/17208.misc
new file mode 100644
index 0000000000..142300b1f2
--- /dev/null
+++ b/changelog.d/17208.misc
@@ -0,0 +1 @@
+Rename to be obvious: `joined_rooms` -> `joined_room_ids`.
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 6d4373008c..6634b3887e 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -1875,7 +1875,7 @@ class SyncHandler:
                 # or if the changed user is the syncing user (as we always
                 # want to include device list updates of their own devices).
                 if user_id == changed_user_id or any(
-                    rid in joined_rooms for rid in entries
+                    rid in joined_room_ids for rid in entries
                 ):
                     users_that_have_changed.add(changed_user_id)
         else: