--- a/mercurial/configitems.py	Fri Jun 30 03:42:27 2017 +0200
+++ b/mercurial/configitems.py	Fri Jun 30 03:42:28 2017 +0200
@@ -125,6 +125,9 @@
 coreconfigitem('format', 'obsstore-version',
     default=None,
 )
+coreconfigitem('format', 'usefncache',
+    default=True,
+)
 coreconfigitem('hostsecurity', 'ciphers',
     default=None,
 )

--- a/mercurial/localrepo.py	Fri Jun 30 03:42:27 2017 +0200
+++ b/mercurial/localrepo.py	Fri Jun 30 03:42:28 2017 +0200
@@ -2076,7 +2076,7 @@
     requirements = {'revlogv1'}
     if ui.configbool('format', 'usestore', True):
         requirements.add('store')
-        if ui.configbool('format', 'usefncache', True):
+        if ui.configbool('format', 'usefncache'):
             requirements.add('fncache')
             if ui.configbool('format', 'dotencode'):
                 requirements.add('dotencode')