diff --git a/src/_zkapauthorizer/_storage_server.py b/src/_zkapauthorizer/_storage_server.py
index e535ff6412844db1b5a29a3f0c96a140ced50cf7..04609e3cd325924401a81815214b71bd5ded3162 100644
--- a/src/_zkapauthorizer/_storage_server.py
+++ b/src/_zkapauthorizer/_storage_server.py
@@ -33,12 +33,9 @@ from struct import calcsize, unpack
 import attr
 from allmydata.interfaces import RIStorageServer
 from allmydata.storage.common import storage_index_to_dir
-from allmydata.storage.shares import get_share_file
-
 from allmydata.storage.immutable import ShareFile
 from allmydata.storage.mutable import MutableShareFile
-
-
+from allmydata.storage.shares import get_share_file
 from allmydata.util.base32 import b2a
 from attr.validators import instance_of, provides
 from challenge_bypass_ristretto import SigningKey, TokenPreimage, VerificationSignature
@@ -642,6 +639,7 @@ def stat_slot(storage_server, slot, sharepath):
         lease_expiration=get_lease_expiration(sharepath),
     )
 
+
 def get_lease_expiration(sharepath):
     # type: (str) -> Optional[int]
     """
@@ -651,14 +649,13 @@ def get_lease_expiration(sharepath):
     :param sharepath: The path to the share file to inspect.
     """
     leases = list(
-        lease.get_expiration_time()
-        for lease
-        in get_share_file(sharepath).get_leases()
+        lease.get_expiration_time() for lease in get_share_file(sharepath).get_leases()
     )
     if leases:
         return max(leases)
     return None
 
+
 def get_slot_share_size(sharepath):
     """
     Get the size of a share belonging to a slot (a mutable share).
diff --git a/src/_zkapauthorizer/tests/test_lease_maintenance.py b/src/_zkapauthorizer/tests/test_lease_maintenance.py
index a81b78da4f8854c38f298169f47f898d28d93081..e79e7c40b3c91c4d97483c0129ea177c18a09129 100644
--- a/src/_zkapauthorizer/tests/test_lease_maintenance.py
+++ b/src/_zkapauthorizer/tests/test_lease_maintenance.py
@@ -34,10 +34,10 @@ from hypothesis.strategies import (
     floats,
     integers,
     just,
-    tuples,
     lists,
-    sets,
     randoms,
+    sets,
+    tuples,
 )
 from testtools import TestCase
 from testtools.matchers import (
@@ -66,7 +66,13 @@ from ..lease_maintenance import (
     visit_storage_indexes_from_root,
 )
 from .matchers import Provides, between, leases_current
-from .strategies import clocks, posix_timestamps, node_hierarchies, storage_indexes, sharenums
+from .strategies import (
+    clocks,
+    node_hierarchies,
+    posix_timestamps,
+    sharenums,
+    storage_indexes,
+)
 
 
 def interval_means():
@@ -100,17 +106,12 @@ class DummyStorageServer(object):
     """
 
     clock = attr.ib()
-    buckets = attr.ib() # type: Dict[bytes, Dict[int, ShareStat]]
+    buckets = attr.ib()  # type: Dict[bytes, Dict[int, ShareStat]]
     lease_seed = attr.ib()
 
     def stat_shares(self, storage_indexes):
         # type: (List[bytes]) -> Deferred[List[Dict[int, ShareStat]]]
-        return succeed(
-            list(
-                self.buckets.get(idx, {})
-                for idx in storage_indexes
-            )
-        )
+        return succeed(list(self.buckets.get(idx, {}) for idx in storage_indexes))
 
     def get_lease_seed(self):
         return self.lease_seed
@@ -440,6 +441,7 @@ def lists_of_buckets():
     share numbers to lease expiration times (as posix timestamps).  Any given
     storage index will appear only once in the overall result.
     """
+
     def add_expiration_times(sharenums):
         return builds(
             lambda nums, expires: dict(zip(nums, expires)),
@@ -634,7 +636,9 @@ class MaintainLeasesFromRootTests(TestCase):
         for node in root_node.flatten():
             for server in storage_broker.get_connected_servers():
                 try:
-                    shares = server.get_storage_server().buckets[node.get_storage_index()]
+                    shares = server.get_storage_server().buckets[
+                        node.get_storage_index()
+                    ]
                 except KeyError:
                     continue
                 else: