diff -r 592a3cc1ebc4 -r 0314e02efa25 mercurial/localrepo.py
--- a/mercurial/localrepo.py	Sun Oct 08 20:16:09 2017 +0200
+++ b/mercurial/localrepo.py	Sun Oct 08 20:42:19 2017 +0200
@@ -601,7 +601,7 @@
                                                    'aggressivemergedeltas')
         self.svfs.options['aggressivemergedeltas'] = aggressivemergedeltas
         self.svfs.options['lazydeltabase'] = not scmutil.gddeltaconfig(self.ui)
-        chainspan = self.ui.configbytes('experimental', 'maxdeltachainspan', -1)
+        chainspan = self.ui.configbytes('experimental', 'maxdeltachainspan')
         if 0 <= chainspan:
             self.svfs.options['maxdeltachainspan'] = chainspan
         mmapindexthreshold = self.ui.configbytes('experimental',