diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -113,6 +113,9 @@ coreconfigitem('hostsecurity', 'disablet
 coreconfigitem('patch', 'fuzz',
     default=2,
 )
+coreconfigitem('server', 'bundle1',
+    default=True,
+)
 coreconfigitem('ui', 'clonebundleprefers',
     default=list,
 )
diff --git a/mercurial/wireproto.py b/mercurial/wireproto.py
--- a/mercurial/wireproto.py
+++ b/mercurial/wireproto.py
@@ -608,7 +608,7 @@ def bundle1allowed(repo, action):
         if v is not None:
             return v
 
-    return ui.configbool('server', 'bundle1', True)
+    return ui.configbool('server', 'bundle1')
 
 def supportedcompengines(ui, proto, role):
     """Obtain the list of supported compression engines for a request."""