diff --git a/zarr/storage.py b/zarr/storage.py
index 821d0a3bf3..62f68fe3bc 100644
--- a/zarr/storage.py
+++ b/zarr/storage.py
@@ -14,6 +14,7 @@
 path) and a `getsize` method (return the size in bytes of a given value).
 
 """
+
 import atexit
 import errno
 import glob
@@ -1410,8 +1411,8 @@ def _normalize_key(self, key):
                 self._attrs_key,
                 ".zmetadata",  # see: #1121
             ):
-                end = end.replace('.', self.key_separator)
-                key = '/'.join(bits + [end])
+                end = end.replace(".", self.key_separator)
+                key = "/".join(bits + [end])
 
         return key.lower() if self.normalize_keys else key