diff -r faca3f5c1848 lib/keep.py
--- a/lib/keep.py	Tue Nov 10 10:41:41 2009 -0800
+++ b/lib/keep.py	Tue Jun 08 10:00:28 2010 -0700
@@ -94,11 +94,11 @@
 
     __slots__ = []
 
-    def __init__(self, value_spec=Keyed, mapping_class=BTree):
+    def __init__(self, value_spec=Keyed, mapping_class=BTree, counter_class=Counter):
         assert isinstance(self, PersistentObject)
         self.mapping = mapping_class()
         self.value_spec = value_spec
-        self.set_counter(Counter())
+        specify(self, key_counter=counter_class())
 
     def set_counter(self, counter):
         specify(self, key_counter=counter)