diff --git a/test/test_persistent_dict.py b/test/test_persistent_dict.py
index cae1c33302314eae471a0a31cd8c7e6abf47837f..9079d58f4671fb720ccab12ee310a9ddc20cde03 100644
--- a/test/test_persistent_dict.py
+++ b/test/test_persistent_dict.py
@@ -16,7 +16,7 @@ def test_persistent_dict():
                 chr(65+randrange(26))
                 for i in range(n))
 
-    keys = [(randrange(2000), rand_str()) for i in range(20)]
+    keys = [(randrange(2000), rand_str(), None) for i in range(20)]
     values = [randrange(2000) for i in range(20)]
 
     d = dict(zip(keys, values))