diff -r a2dfe82f27a0 -r 8be3973adf34 hgext/obsolete.py
--- a/hgext/obsolete.py	Mon Aug 20 19:12:20 2012 +0200
+++ b/hgext/obsolete.py	Tue Aug 21 02:25:19 2012 +0200
@@ -956,6 +956,9 @@
 def buildstate(orig, repo, dest, rebaseset, *ags, **kws):
     """wrapper for rebase 's buildstate that exclude obsolete changeset"""
     rebaseset = repo.revs('%ld - extinct()', rebaseset)
+    if not rebaseset:
+        repo.ui.warn(_('whole rebase set is extinct and ignored.\n'))
+        return {}
     return orig(repo, dest, rebaseset, *ags, **kws)
 
 def defineparents(orig, repo, rev, target, state, *args, **kwargs):