diff --git a/synapse/push/bulk_push_rule_evaluator.py b/synapse/push/bulk_push_rule_evaluator.py
index 6459eec22..ca3b5af80 100644
--- a/synapse/push/bulk_push_rule_evaluator.py
+++ b/synapse/push/bulk_push_rule_evaluator.py
@@ -112,9 +112,15 @@ class BulkPushRuleEvaluator(object):
 
     @defer.inlineCallbacks
     def _get_sender_power_level(self, event, context):
-        auth_events_ids = yield self.auth.compute_auth_events(
-            event, context.prev_state_ids, for_verification=False,
-        )
+        pl_event_key = (EventTypes.PowerLevels, "", )
+        if pl_event_key in context.prev_state_ids:
+            # fastpath: if there's a power level event, that's all we need, and
+            # not having a power level event is an extreme edge case
+            auth_events_ids = [context.prev_state_ids[pl_event_key]]
+        else:
+            auth_events_ids = yield self.auth.compute_auth_events(
+                event, context.prev_state_ids, for_verification=False,
+            )
         auth_events = yield self.store.get_events(auth_events_ids)
         auth_events = {
             (e.type, e.state_key): e for e in auth_events.values()