1 files changed, 2 insertions, 0 deletions
diff --git a/synapse/handlers/device.py b/synapse/handlers/device.py
index 544bc7c13d..3ce96ef3cb 100644
--- a/synapse/handlers/device.py
+++ b/synapse/handlers/device.py
@@ -592,6 +592,8 @@ class DeviceHandler(DeviceWorkerHandler):
                 )
 
             # Delete device messages asynchronously and in batches using the task scheduler
+            # We specify an upper stream id to avoid deleting non delivered messages
+            # if an user re-uses a device ID.
             await self._task_scheduler.schedule_task(
                 DELETE_DEVICE_MSGS_TASK_NAME,
                 resource_id=device_id,