diff -Nru mercurial-1.9.1/debian/changelog mercurial-1.9.1/debian/changelog
--- mercurial-1.9.1/debian/changelog	2011-08-03 09:01:23.000000000 +0200
+++ mercurial-1.9.1/debian/changelog	2011-10-17 23:24:41.000000000 +0200
@@ -1,3 +1,10 @@
+mercurial (1.9.1-1ubuntu0.1) oneiric-proposed; urgency=low
+
+  * Apply upstream patch to bundlerepo, to check the bundlename argument
+    before unlinking it. (LP: #831313)
+
+ -- Stefano Rivera <stefanor@ubuntu.com>  Mon, 17 Oct 2011 23:22:42 +0200
+
 mercurial (1.9.1-1) unstable; urgency=low
 
   * Convert to dh_python2
diff -Nru mercurial-1.9.1/debian/patches/backport_upstream__none-bundlerepo mercurial-1.9.1/debian/patches/backport_upstream__none-bundlerepo
--- mercurial-1.9.1/debian/patches/backport_upstream__none-bundlerepo	1970-01-01 02:00:00.000000000 +0200
+++ mercurial-1.9.1/debian/patches/backport_upstream__none-bundlerepo	2011-10-17 23:23:14.000000000 +0200
@@ -0,0 +1,22 @@
+Description: bundlerepo: add argument check before unlink
+ The default argument value of None, for bundlename, would cause an exception.
+ Callers currently pass an empty string, thus dodging this problem.
+ Upstream commit: 106f89299da61291b31dc054de721c98a04a1380
+Origin: upstream, http://selenic.com/hg/rev/106f89299da61291b31dc054de721c98a04a1380
+Author: Sune Foldager <cryo@cyanite.org>
+Bug-Ubuntu: https://bugs.launchpad.net/bug/831313
+Acked-by: Stefano Rivera <stefanor@ubuntu.com>
+Last-Update: 2011-10-17
+
+--- a/mercurial/bundlerepo.py
++++ b/mercurial/bundlerepo.py
+@@ -315,7 +315,8 @@
+     common, incoming, rheads = tmp
+     if not incoming:
+         try:
+-            os.unlink(bundlename)
++            if bundlename:
++                os.unlink(bundlename)
+         except OSError:
+             pass
+         return other, [], other.close
diff -Nru mercurial-1.9.1/debian/patches/series mercurial-1.9.1/debian/patches/series
--- mercurial-1.9.1/debian/patches/series	2011-07-30 20:17:47.000000000 +0200
+++ mercurial-1.9.1/debian/patches/series	2011-10-17 23:20:16.000000000 +0200
@@ -6,3 +6,4 @@
 proposed_upstream__correct-zeroconf-doc
 deb_specific__install-mo-fhs.patch
 deb_specific__disable_libdir_replacement.patch
+backport_upstream__none-bundlerepo