diff --git a/mercurial/configitems.py b/mercurial/configitems.py
index e7701286f7..029582382c 100644
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -164,3 +164,6 @@ coreconfigitem('worker', 'backgroundcloseminfilecount',
 coreconfigitem('worker', 'backgroundclosethreadcount',
     default=4,
 )
+coreconfigitem('worker', 'numcpus',
+    default=None,
+)