diff --git a/substanced/catalog/subscribers.py b/substanced/catalog/subscribers.py
index ef281589..d7d58f4a 100644
--- a/substanced/catalog/subscribers.py
+++ b/substanced/catalog/subscribers.py
@@ -1,3 +1,4 @@
+import BTrees
 from zope.interface import Interface
 
 from pyramid.events import subscriber
@@ -33,9 +34,8 @@ def object_will_be_removed(obj, event):
     if objectmap is None or catalog is None:
         return
     objectids = objectmap.pathlookup(obj)
-    for oid in objectids:
-        if oid in catalog.objectids:
-            catalog.unindex_doc(oid)
+    for oid in BTrees.family32.IF.intersection(objectids, catalog.objectids):
+        catalog.unindex_doc(oid)
 
 @subscriber([Interface, IObjectModifiedEvent])
 def object_modified(obj, event):
diff --git a/substanced/catalog/tests/test_subscribers.py b/substanced/catalog/tests/test_subscribers.py
index 141dd876..033aea22 100644
--- a/substanced/catalog/tests/test_subscribers.py
+++ b/substanced/catalog/tests/test_subscribers.py
@@ -1,11 +1,10 @@
 import unittest
+import BTrees
 
 from zope.interface import alsoProvides
 
 from pyramid import testing
 
-from pyramid.traversal import resource_path_tuple
-
 def _makeSite(**kw):
     from ...interfaces import IFolder
     site = testing.DummyResource(__provides__=kw.pop('__provides__', None))
@@ -75,7 +74,7 @@ def test_no_catalog(self):
     def test_with_pathlookup(self):
         model = testing.DummyResource()
         catalog = DummyCatalog()
-        catalog.objectids = [1,2]
+        catalog.objectids = BTrees.family32.IF.Set([1,2])
         objectmap = DummyObjectMap()
         site = _makeSite(objectmap=objectmap, catalog=catalog)
         site['model'] = model
@@ -87,7 +86,7 @@ def test_with_pathlookup(self):
     def test_with_pathlookup_limited_by_objectids(self):
         model = testing.DummyResource()
         catalog = DummyCatalog()
-        catalog.objectids = [1]
+        catalog.objectids = BTrees.family32.IF.Set([1])
         objectmap = DummyObjectMap()
         site = _makeSite(objectmap=objectmap, catalog=catalog)
         site['model'] = model
@@ -154,7 +153,7 @@ def reindex_doc(self, objectid, obj):
 
 class DummyObjectMap:
     def pathlookup(self, obj):
-        return [1,2]
+        return BTrees.family32.IF.Set([1,2])
 
 class DummyEvent(object):
     def __init__(self, parent):