diff -r 2abffea40700 -r b958419b6c53 mercurial/localrepo.py
--- a/mercurial/localrepo.py	Mon Dec 23 17:47:31 2019 +0100
+++ b/mercurial/localrepo.py	Wed Jan 08 20:23:24 2020 -0500
@@ -927,7 +927,7 @@
     if repository.NARROW_REQUIREMENT in requirements:
         options[b'enableellipsis'] = True
 
-    if ui.configbool('experimental', 'rust.index'):
+    if ui.configbool(b'experimental', b'rust.index'):
         options[b'rust.index'] = True
 
     return options