diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index f1fbb3d14a..7154bcbea6 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -93,7 +93,7 @@ class _EventInternalMetadata(object):
         return getattr(self, "soft_failed", False)
 
     def should_proactively_send(self):
-        """Whether the eventm, if ours, should be sent to other clients and
+        """Whether the event, if ours, should be sent to other clients and
         servers.
 
         This is used for sending dummy events internally. Servers and clients
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 3b5942b7ae..7728ea230d 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -34,6 +34,7 @@ from synapse.api.errors import (
 from synapse.api.room_versions import RoomVersions
 from synapse.api.urls import ConsentURIBuilder
 from synapse.events.validator import EventValidator
+from synapse.metrics.background_process_metrics import run_as_background_process
 from synapse.replication.http.send_event import ReplicationSendEventRestServlet
 from synapse.storage.state import StateFilter
 from synapse.types import RoomAlias, UserID, create_requester
@@ -265,9 +266,11 @@ class EventCreationHandler(object):
             not self.config.worker_app
             and self.config.cleanup_extremities_with_dummy_events
         ):
-            # XXX: Send dummy events.
             self.clock.looping_call(
-                self._send_dummy_events_to_fill_extremities,
+                lambda: run_as_background_process(
+                    "send_dummy_events_to_fill_extremities",
+                    self._send_dummy_events_to_fill_extremities
+                ),
                 5 * 60 * 1000,
             )
 
diff --git a/tests/storage/test_cleanup_extrems.py b/tests/storage/test_cleanup_extrems.py
index ed5d58f58c..e9e2d5337c 100644
--- a/tests/storage/test_cleanup_extrems.py
+++ b/tests/storage/test_cleanup_extrems.py
@@ -255,7 +255,7 @@ class CleanupExtremDummyEventsTestCase(HomeserverTestCase):
         )
         self.assertEqual(len(latest_event_ids), 50)
 
-        # Bump the reacto repeatedly so that the background updates have a
+        # Pump the reactor repeatedly so that the background updates have a
         # chance to run.
         self.pump(10 * 60)