diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index 48548f8c4082..9989b7659179 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -154,7 +154,8 @@ def serialize_event(e, time_now_ms, as_client_event=True,
 
     if "redacted_because" in e.unsigned:
         d["unsigned"]["redacted_because"] = serialize_event(
-            e.unsigned["redacted_because"], time_now_ms
+            e.unsigned["redacted_because"], time_now_ms,
+            event_format=event_format
         )
 
     if token_id is not None:
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 04f2d46d1524..4c5a2353b2be 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -520,7 +520,7 @@ def incremental_sync_with_gap_for_room(self, room_id, sync_config,
             current_state=current_state_events,
         )
 
-        state_events_delta = yield self.check_joined_room(
+        state_events_delta, _ = yield self.check_joined_room(
             sync_config, room_id, state_events_delta
         )
 
diff --git a/tox.ini b/tox.ini
index a69948484f63..01b23e6bd967 100644
--- a/tox.ini
+++ b/tox.ini
@@ -19,6 +19,7 @@ commands =
     check-manifest
 
 [testenv:pep8]
+skip_install = True
 basepython = python2.7
 deps =
     flake8