diff --git a/zerver/actions/streams.py b/zerver/actions/streams.py
index e8699a711f..eabf38dbe4 100644
--- a/zerver/actions/streams.py
+++ b/zerver/actions/streams.py
@@ -530,7 +530,7 @@ def send_peer_subscriber_events(
                     # This optimization depends on all public streams
                     # having the same peers for any single user, which
                     # isn't the case for private streams.
-                    altered_user_id = list(altered_user_ids)[0]
+                    [altered_user_id] = altered_user_ids
                     user_streams[altered_user_id].add(stream_id)
                 else:
                     event = dict(