diff -r 3bd8ab4c80a5 -r e5b6ba786d83 mercurial/commands.py
--- a/mercurial/commands.py	Sun Oct 15 23:08:45 2017 +0530
+++ b/mercurial/commands.py	Fri Jan 19 18:45:20 2018 +0530
@@ -1055,11 +1055,6 @@
 
             scmutil.checknewlabel(repo, label, 'branch')
             if revs:
-                # XXX: we should allow setting name to existing branch if the
-                # branch of root of the revs is same as the new branch name
-                if label in repo.branchmap():
-                    raise error.Abort(_('a branch of the same'
-                                        ' name already exists'))
                 return cmdutil.changebranch(ui, repo, revs, label)
 
             if not opts.get('force') and label in repo.branchmap():