diff --git a/src/_zkapauthorizer/_storage_server.py b/src/_zkapauthorizer/_storage_server.py
index b78a7c4f4fde0c06d2e25ebdfa54519cedd79165..39fdbbb412769b31a2eb0598ce1d27f81ad97b3e 100644
--- a/src/_zkapauthorizer/_storage_server.py
+++ b/src/_zkapauthorizer/_storage_server.py
@@ -68,7 +68,10 @@ except ImportError:
 # Hack around a bug in prometheus_client
 def _prometheus_client_fix():
     import prometheus_client.exposition
+
     prometheus_client.exposition.FileNotFoundError = IOError
+
+
 _prometheus_client_fix()
 
 # See allmydata/storage/mutable.py