diff --git a/eve/io/mongo/mongo.py b/eve/io/mongo/mongo.py
index 8d9fce156..b84f4bc9b 100644
--- a/eve/io/mongo/mongo.py
+++ b/eve/io/mongo/mongo.py
@@ -856,9 +856,7 @@ def dict_sub_schema(base):
                         return next((t for t in possible_types if t), None)
                 elif "schema" in schema[k]:
                     # recursively check the schema
-                    return get_schema_type(
-                        keys, dict_sub_schema(schema[k]["schema"])
-                    )
+                    return get_schema_type(keys, dict_sub_schema(schema[k]["schema"]))
             elif schema_type == "dict":
                 if "schema" in schema[k]:
                     return get_schema_type(keys, dict_sub_schema(schema[k]["schema"]))