diff --git a/moto/cognitoidp/responses.py b/moto/cognitoidp/responses.py
index a170b7541..fa3b7b0b5 100644
--- a/moto/cognitoidp/responses.py
+++ b/moto/cognitoidp/responses.py
@@ -284,8 +284,13 @@ class CognitoIdpResponse(BaseResponse):
             user_pool_id, limit=limit, pagination_token=token
         )
         if filt:
-            name, value = filt.replace('"', '').split('=')
-            users = [user for user in users for attribute in user.attributes if attribute['Name'] == name and attribute['Value'] == value]
+            name, value = filt.replace('"', "").split("=")
+            users = [
+                user
+                for user in users
+                for attribute in user.attributes
+                if attribute["Name"] == name and attribute["Value"] == value
+            ]
         response = {"Users": [user.to_json(extended=True) for user in users]}
         if token:
             response["PaginationToken"] = str(token)
diff --git a/tests/test_cognitoidp/test_cognitoidp.py b/tests/test_cognitoidp/test_cognitoidp.py
index 27a6841f4..2f7ed11e5 100644
--- a/tests/test_cognitoidp/test_cognitoidp.py
+++ b/tests/test_cognitoidp/test_cognitoidp.py
@@ -960,10 +960,13 @@ def test_list_users():
 
     username_bis = str(uuid.uuid4())
     conn.admin_create_user(
-        UserPoolId=user_pool_id, Username=username_bis,
-        UserAttributes=[{'Name': 'phone_number', 'Value': '+33666666666'}]
+        UserPoolId=user_pool_id,
+        Username=username_bis,
+        UserAttributes=[{"Name": "phone_number", "Value": "+33666666666"}],
+    )
+    result = conn.list_users(
+        UserPoolId=user_pool_id, Filter='phone_number="+33666666666'
     )
-    result = conn.list_users(UserPoolId=user_pool_id, Filter='phone_number="+33666666666')
     result["Users"].should.have.length_of(1)
     result["Users"][0]["Username"].should.equal(username_bis)