diff -r 32ea809e5bd1 -r af8db3b42a4a mercurial/commands.py
--- a/mercurial/commands.py	Thu May 17 20:09:49 2007 -0700
+++ b/mercurial/commands.py	Thu May 17 20:09:52 2007 -0700
@@ -1547,6 +1547,7 @@
                 if p1 != wp[0].node():
                     hg.clean(repo, p1, wlock=wlock)
                 repo.dirstate.setparents(p1, p2)
+                repo.dirstate.setbranch(branch or 'default')
             elif p2:
                 try:
                     p1 = repo.lookup(p1)