--- a/mercurial/changelog.py	Wed Nov 05 09:27:08 2014 +0000
+++ b/mercurial/changelog.py	Sat Nov 08 17:08:09 2014 +0000
@@ -273,7 +273,11 @@
         if self._delaybuf:
             # make a temporary copy of the index
             fp1 = self._realopener(self.indexfile)
-            fp2 = self._realopener(self.indexfile + ".a", "w")
+            pendingfilename = self.indexfile + ".a"
+            # register as a temp file to ensure cleanup on failure
+            tr.registertmp(pendingfilename)
+            # write existing data
+            fp2 = self._realopener(pendingfilename, "w")
             fp2.write(fp1.read())
             # add pending data
             fp2.write("".join(self._delaybuf))

--- a/tests/test-hook.t	Wed Nov 05 09:27:08 2014 +0000
+++ b/tests/test-hook.t	Sat Nov 08 17:08:09 2014 +0000
@@ -148,6 +148,19 @@
   $ hg -q tip
   4:539e4b31b6dc
 
+(Check that no 'changelog.i.a' file were left behind)
+
+  $ ls -1 .hg/store/
+  00changelog.i
+  00manifest.i
+  data
+  fncache
+  journal.phaseroots
+  phaseroots
+  undo
+  undo.phaseroots
+
+
 precommit hook can prevent commit
 
   $ echo "precommit.forbid = python \"$TESTDIR/printenv.py\" precommit.forbid 1" >> .hg/hgrc