--- a/mercurial/configitems.py	Wed Aug 15 22:24:38 2018 +0900
+++ b/mercurial/configitems.py	Wed Aug 15 22:24:50 2018 +0900
@@ -771,6 +771,9 @@
 coreconfigitem('merge', 'preferancestor',
         default=lambda: ['*'],
 )
+coreconfigitem('merge', 'strict-capability-check',
+    default=False,
+)
 coreconfigitem('merge-tools', '.*',
     default=None,
     generic=True,