diff --git a/hgext/obsolete.py b/hgext/obsolete.py
index b836862d48b44857b8991b7241776604bf86b02c_aGdleHQvb2Jzb2xldGUucHk=..4ecbaec1d664b1e6f8ebc78292e1ced77a8e69c0_aGdleHQvb2Jzb2xldGUucHk= 100644
--- a/hgext/obsolete.py
+++ b/hgext/obsolete.py
@@ -756,6 +756,7 @@
     while toproceed:
         current = toproceed.pop()
         assert len(current) <= 1, 'splitting not handled yet. %r' % current
+        current = [n for n in current if n != nullid]
         if current:
             n, = current
             if n in objectrels: