diff --git a/mongoengine/queryset.py b/mongoengine/queryset.py
index d55c5f7a..11c7a804 100644
--- a/mongoengine/queryset.py
+++ b/mongoengine/queryset.py
@@ -122,7 +122,6 @@ class QueryTreeTransformerVisitor(QNodeVisitor):
                 q_object = reduce(lambda a, b: a & b, and_parts, Q())
                 q_object = reduce(lambda a, b: a & b, or_group, q_object)
                 clauses.append(q_object)
-
             # Finally, $or the generated clauses in to one query. Each of the
             # clauses is sufficient for the query to succeed.
             return reduce(lambda a, b: a | b, clauses, Q())
@@ -431,6 +430,11 @@ class QuerySet(object):
 
         return spec
 
+    @classmethod
+    def _reset_already_indexed(cls):
+        """Helper to reset already indexed, can be useful for testing purposes"""
+        cls.__already_indexed = set()
+
     def __call__(self, q_obj=None, class_check=True, slave_okay=False, **query):
         """Filter the selected documents by calling the
         :class:`~mongoengine.queryset.QuerySet` with a query.