--- a/mercurial/commands.py	Tue Feb 28 10:06:35 2012 +0100
+++ b/mercurial/commands.py	Tue Feb 28 23:47:46 2012 +0200
@@ -5732,6 +5732,8 @@
             ui.status(_("updating bookmark %s\n") % repo._bookmarkcurrent)
     elif brev in repo._bookmarks:
         bookmarks.setcurrent(repo, brev)
+    elif brev:
+        bookmarks.unsetcurrent(repo)
 
     return ret