--- a/mercurial/commands.py	Sun Feb 26 17:12:15 2012 +0100
+++ b/mercurial/commands.py	Tue Feb 28 21:17:53 2012 -0600
@@ -5720,7 +5720,7 @@
 
     # with no argument, we also move the current bookmark, if any
     movemarkfrom = None
-    if node is None or node == '':
+    if rev is None or node == '':
         movemarkfrom = repo['.'].node()
 
     # if we defined a bookmark, we have to remember the original bookmark name
@@ -5754,6 +5754,8 @@
             ui.status(_("updating bookmark %s\n") % repo._bookmarkcurrent)
     elif brev in repo._bookmarks:
         bookmarks.setcurrent(repo, brev)
+    elif brev:
+        bookmarks.unsetcurrent(repo)
 
     return ret