diff --git a/zerver/lib/notification_data.py b/zerver/lib/notification_data.py
index 6ec0e6b550..db59f6de4e 100644
--- a/zerver/lib/notification_data.py
+++ b/zerver/lib/notification_data.py
@@ -1,11 +1,11 @@
 from dataclasses import dataclass
-from typing import List
+from typing import Collection
 
 
 @dataclass
 class UserMessageNotificationsData:
     id: int
-    flags: List[str]
+    flags: Collection[str]
     mentioned: bool
     online_push_enabled: bool
     stream_push_notify: bool
diff --git a/zerver/tornado/event_queue.py b/zerver/tornado/event_queue.py
index 8f02e4b42b..a65d25048c 100644
--- a/zerver/tornado/event_queue.py
+++ b/zerver/tornado/event_queue.py
@@ -948,7 +948,7 @@ def process_message_event(
 
     for user_data in users:
         user_profile_id: int = user_data["id"]
-        flags: Iterable[str] = user_data.get("flags", [])
+        flags: Collection[str] = user_data.get("flags", [])
 
         # If the recipient was offline and the message was a single or group PM to them
         # or they were @-notified potentially notify more immediately