--- a/mercurial/error.py	Wed Oct 15 16:14:50 2014 -0700
+++ b/mercurial/error.py	Wed Oct 15 17:02:44 2014 -0700
@@ -16,6 +16,9 @@
 class RevlogError(Exception):
     pass
 
+class FilteredIndexError(IndexError):
+    pass
+
 class LookupError(RevlogError, KeyError):
     def __init__(self, name, index, message):
         self.name = name