diff -r 832c98d79587 -r 45b86dbabbda mercurial/commands.py
--- a/mercurial/commands.py	Mon Oct 12 19:22:34 2015 +0200
+++ b/mercurial/commands.py	Mon Oct 05 03:50:47 2015 -0700
@@ -20,7 +20,7 @@
 import minirst, revset, fileset
 import dagparser, context, simplemerge, graphmod, copies
 import random, operator
-import setdiscovery, treediscovery, dagutil, pvec, localrepo
+import setdiscovery, treediscovery, dagutil, pvec, localrepo, destutil
 import phases, obsolete, exchange, bundle2, repair, lock as lockmod
 import ui as uimod
 
@@ -6597,6 +6597,8 @@
             cmdutil.bailifchanged(repo, merge=False)
             if rev is None:
                 rev = repo[repo[None].branch()].rev()
+        elif rev is None:
+            rev = destutil.destupdate(repo, clean=clean)
 
         repo.ui.setconfig('ui', 'forcemerge', tool, 'update')