diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index be88328ce..0859518b1 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -566,6 +566,7 @@ class EventsStore(SQLBaseStore):
                     "do_fetch",
                     do_fetch
                 )
+                self._event_fetch_ongoing = True
 
         res = yield d