diff --git a/synapse/util/frozenutils.py b/synapse/util/frozenutils.py
index 97914907aa..15f0a7ba9e 100644
--- a/synapse/util/frozenutils.py
+++ b/synapse/util/frozenutils.py
@@ -18,6 +18,7 @@ import simplejson as json
 
 from six import string_types
 
+
 def freeze(o):
     if isinstance(o, dict):
         return frozendict({k: freeze(v) for k, v in o.items()})