diff --git a/django/db/models/query.py b/django/db/models/query.py
index c5e0f819c4..1cacd9b59e 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -288,7 +288,7 @@ class QuerySet(object):
         combined = other._clone()
         # If 'self' is ordered and 'other' isn't, propagate 'self's ordering
         if (self._order_by is not None and len(self._order_by) > 0) and \
-           (combined._order_by is None or len(combined._order_by == 0)):
+           (combined._order_by is None or len(combined._order_by) == 0):
             combined._order_by = self._order_by
         return combined