diff --git a/mercurial/changelog.py b/mercurial/changelog.py
--- a/mercurial/changelog.py
+++ b/mercurial/changelog.py
@@ -179,7 +179,7 @@ class changelog(revlog):
 
         user = user.strip()
         if "\n" in user:
-            raise RevlogError(_("username %s contains a newline") % `user`)
+            raise RevlogError(_("username %s contains a newline") % repr(user))
         user, desc = util.fromlocal(user), util.fromlocal(desc)
 
         if date:
diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -350,7 +350,7 @@ class ui(object):
         if not user:
             raise util.Abort(_("Please specify a username."))
         if "\n" in user:
-            raise util.Abort(_("username %s contains a newline\n") % `user`)
+            raise util.Abort(_("username %s contains a newline\n") % repr(user))
         return user
 
     def shortuser(self, user):