--- a/mercurial/commands.py	Fri Nov 14 13:48:23 2008 +0100
+++ b/mercurial/commands.py	Fri Nov 14 14:36:17 2008 +0100
@@ -2091,7 +2091,7 @@
     if modheads == 0:
         return
     if optupdate:
-        if modheads <= 1 or checkout:
+        if (modheads <= 1 or len(repo.branchheads()) == 1) or checkout:
             return hg.update(repo, checkout)
         else:
             ui.status(_("not updating, since new heads added\n"))