diff --git a/synapse/storage/events.py b/synapse/storage/events.py
index 552e7ca35..285c586cf 100644
--- a/synapse/storage/events.py
+++ b/synapse/storage/events.py
@@ -526,6 +526,9 @@ class EventsStore(SQLBaseStore):
         if not event_ids:
             defer.returnValue([])
 
+        event_id_list = event_ids
+        event_ids = set(event_ids)
+
         event_map = self._get_events_from_cache(
             event_ids,
             check_redacted=check_redacted,
@@ -535,23 +538,18 @@ class EventsStore(SQLBaseStore):
 
         missing_events_ids = [e for e in event_ids if e not in event_map]
 
-        if not missing_events_ids:
-            defer.returnValue([
-                event_map[e_id] for e_id in event_ids
-                if e_id in event_map and event_map[e_id]
-            ])
+        if missing_events_ids:
+            missing_events = yield self._enqueue_events(
+                missing_events_ids,
+                check_redacted=check_redacted,
+                get_prev_content=get_prev_content,
+                allow_rejected=allow_rejected,
+            )
 
-        missing_events = yield self._enqueue_events(
-            missing_events_ids,
-            check_redacted=check_redacted,
-            get_prev_content=get_prev_content,
-            allow_rejected=allow_rejected,
-        )
-
-        event_map.update(missing_events)
+            event_map.update(missing_events)
 
         defer.returnValue([
-            event_map[e_id] for e_id in event_ids
+            event_map[e_id] for e_id in event_id_list
             if e_id in event_map and event_map[e_id]
         ])