diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -632,6 +632,9 @@ coreconfigitem('ui', 'interactive',
 coreconfigitem('ui', 'interface',
     default=None,
 )
+coreconfigitem('ui', 'interface.chunkselector',
+    default=None,
+)
 coreconfigitem('ui', 'logblockedtimes',
     default=False,
 )
diff --git a/mercurial/ui.py b/mercurial/ui.py
--- a/mercurial/ui.py
+++ b/mercurial/ui.py
@@ -1149,7 +1149,7 @@ class ui(object):
             defaultinterface = i
 
         choseninterface = defaultinterface
-        f = self.config("ui", "interface.%s" % feature, None)
+        f = self.config("ui", "interface.%s" % feature)
         if f in availableinterfaces:
             choseninterface = f