diff --git a/mongoengine/pymongo_support.py b/mongoengine/pymongo_support.py
index d9c5ee27..3aef4e09 100644
--- a/mongoengine/pymongo_support.py
+++ b/mongoengine/pymongo_support.py
@@ -11,7 +11,9 @@ PYMONGO_VERSION = tuple(pymongo.version_tuple[:2])
 IS_PYMONGO_GTE_37 = PYMONGO_VERSION >= _PYMONGO_37
 
 
-def count_documents(collection, filter, skip=None, limit=None, hint=None, collation=None):
+def count_documents(
+    collection, filter, skip=None, limit=None, hint=None, collation=None
+):
     """Pymongo>3.7 deprecates count in favour of count_documents
     """
     if limit == 0:
diff --git a/mongoengine/queryset/base.py b/mongoengine/queryset/base.py
index 303271f5..ae45297d 100644
--- a/mongoengine/queryset/base.py
+++ b/mongoengine/queryset/base.py
@@ -404,7 +404,7 @@ class BaseQuerySet(object):
 
         if self._limit == 0:
             # mimic the fact that historically .limit(0) sets no limit
-            kwargs.pop('limit', None)
+            kwargs.pop("limit", None)
 
         if self._hint not in (-1, None):
             kwargs["hint"] = self._hint
diff --git a/tests/document/test_indexes.py b/tests/document/test_indexes.py
index 801473b1..5133b007 100644
--- a/tests/document/test_indexes.py
+++ b/tests/document/test_indexes.py
@@ -554,7 +554,7 @@ class TestIndexes(unittest.TestCase):
         incorrect_collation = {"arndom": "wrdo"}
         with pytest.raises(OperationFailure) as exc_info:
             BlogPost.objects.collation(incorrect_collation).count()
-        assert 'Missing expected field' in str(exc_info.value)
+        assert "Missing expected field" in str(exc_info.value)
 
         query_result = BlogPost.objects.collation({}).order_by("name")
         assert [x.name for x in query_result] == sorted(names)