diff --git a/moto/s3/responses.py b/moto/s3/responses.py
index 965d15f5..6ac139a1 100644
--- a/moto/s3/responses.py
+++ b/moto/s3/responses.py
@@ -797,12 +797,12 @@ class ResponseObject(_TemplateEnvironmentMixin, ActionAuthenticatorMixin):
         if hasattr(request, "form"):
             # Not HTTPretty
             form = request.form
-        elif request.headers.get('Content-Type').startswith('multipart/form-data'):
+        elif request.headers.get("Content-Type").startswith("multipart/form-data"):
             request = Request.from_values(
                 input_stream=six.BytesIO(request.body),
-                content_length=request.headers['Content-Length'],
-                content_type=request.headers['Content-Type'],
-                method='POST',
+                content_length=request.headers["Content-Length"],
+                content_type=request.headers["Content-Type"],
+                method="POST",
             )
             form = request.form
         else:
diff --git a/tests/test_s3/test_s3.py b/tests/test_s3/test_s3.py
index c226a7b3..ffbd7396 100644
--- a/tests/test_s3/test_s3.py
+++ b/tests/test_s3/test_s3.py
@@ -4433,30 +4433,37 @@ def test_s3_config_dict():
 
 @mock_s3
 def test_creating_presigned_post():
-    bucket = 'presigned-test'
-    s3 = boto3.client('s3', region_name='us-east-1')
+    bucket = "presigned-test"
+    s3 = boto3.client("s3", region_name="us-east-1")
     s3.create_bucket(Bucket=bucket)
-    success_url = 'http://localhost/completed'
-    fdata = b'test data\n'
+    success_url = "http://localhost/completed"
+    fdata = b"test data\n"
     file_uid = uuid.uuid4()
     conditions = [
-        {"Content-Type": 'text/plain'},
+        {"Content-Type": "text/plain"},
         {"x-amz-server-side-encryption": "AES256"},
-        {'success_action_redirect': success_url},
+        {"success_action_redirect": success_url},
     ]
     conditions.append(["content-length-range", 1, 30])
     data = s3.generate_presigned_post(
         Bucket=bucket,
-        Key='{file_uid}.txt'.format(file_uid=file_uid),
+        Key="{file_uid}.txt".format(file_uid=file_uid),
         Fields={
-            'content-type': 'text/plain',
-            'success_action_redirect': success_url,
-            'x-amz-server-side-encryption': 'AES256'
+            "content-type": "text/plain",
+            "success_action_redirect": success_url,
+            "x-amz-server-side-encryption": "AES256",
         },
         Conditions=conditions,
         ExpiresIn=1000,
     )
-    resp = requests.post(data['url'], data=data['fields'], files={'file': fdata}, allow_redirects=False)
-    assert resp.headers['Location'] == success_url
+    resp = requests.post(
+        data["url"], data=data["fields"], files={"file": fdata}, allow_redirects=False
+    )
+    assert resp.headers["Location"] == success_url
     assert resp.status_code == 303
-    assert s3.get_object(Bucket=bucket, Key='{file_uid}.txt'.format(file_uid=file_uid))['Body'].read() == fdata
+    assert (
+        s3.get_object(Bucket=bucket, Key="{file_uid}.txt".format(file_uid=file_uid))[
+            "Body"
+        ].read()
+        == fdata
+    )