diff --git a/zerver/worker/queue_processors.py b/zerver/worker/queue_processors.py
index 3a8e6e2e73..f6aa3a2eb2 100644
--- a/zerver/worker/queue_processors.py
+++ b/zerver/worker/queue_processors.py
@@ -482,7 +482,9 @@ class UserActivityWorker(LoopQueueProcessingWorker):
                 # This is for compatibility with older events still stuck in the queue,
                 # that used the client name in event["client"] instead of having
                 # event["client_id"] directly.
-                # TODO: This can be deleted for release >= 4.0.
+                #
+                # TODO/compatability: We can delete this once it is no
+                # longer possible to directly upgrade from 2.1 to master.
                 if event["client"] not in self.client_id_map:
                     client = get_client(event["client"])
                     self.client_id_map[event["client"]] = client.id