diff --git a/synapse/storage/background_updates.py b/synapse/storage/background_updates.py
index 321c889b2f..af9bfbbe47 100644
--- a/synapse/storage/background_updates.py
+++ b/synapse/storage/background_updates.py
@@ -88,7 +88,7 @@ class BackgroundUpdateStore(SQLBaseStore):
 
     @defer.inlineCallbacks
     def start_doing_background_updates(self):
-        assert self._background_update_timer is not None, \
+        assert self._background_update_timer is None, \
             "background updates already running"
 
         logger.info("Starting background schema updates")