diff --git a/mongoengine/base/document.py b/mongoengine/base/document.py
index 99c8af87..d05c7695 100644
--- a/mongoengine/base/document.py
+++ b/mongoengine/base/document.py
@@ -19,7 +19,7 @@ from mongoengine.common import _import_class
 from mongoengine.errors import (FieldDoesNotExist, InvalidDocumentError,
                                 LookUpError, OperationError, ValidationError)
 
-__all__ = ('BaseDocument',)
+__all__ = ('BaseDocument', 'NON_FIELD_ERRORS')
 
 NON_FIELD_ERRORS = '__all__'