diff -r 804abe8999f3 -r 39163708825c mercurial/commands.py
--- a/mercurial/commands.py	Sat Nov 28 04:11:38 2015 -0500
+++ b/mercurial/commands.py	Sat Nov 28 04:11:57 2015 -0500
@@ -1617,6 +1617,9 @@
         if not allowunstable and old.children():
             raise error.Abort(_('cannot amend changeset with children'))
 
+        newextra = extra.copy()
+        newextra['branch'] = branch
+        extra = newextra
         # commitfunc is used only for temporary amend commit by cmdutil.amend
         def commitfunc(ui, repo, message, match, opts):
             return repo.commit(message,