diff --git a/mongoengine/base/document.py b/mongoengine/base/document.py
index e5945369..cbe08d61 100644
--- a/mongoengine/base/document.py
+++ b/mongoengine/base/document.py
@@ -18,7 +18,7 @@ from mongoengine.base.datastructures import (BaseDict, BaseList,
 from mongoengine.base.fields import ComplexBaseField
 from mongoengine.common import _import_class
 from mongoengine.errors import (FieldDoesNotExist, InvalidDocumentError,
-                                LookUpError, ValidationError, OperationError)
+                                LookUpError, OperationError, ValidationError)
 from mongoengine.python_support import PY3
 
 __all__ = ('BaseDocument',)