diff --git a/tests/test_state.py b/tests/test_state.py
index c404c0d9ca..610ec9fb46 100644
--- a/tests/test_state.py
+++ b/tests/test_state.py
@@ -152,7 +152,7 @@ class Graph(object):
         return iter(self._events)
 
     def get_leaves(self):
-        return self._events[i] for i in self._leaves
+        return (self._events[i] for i in self._leaves)
 
 
 class StateTestCase(unittest.TestCase):