diff --git a/tools/mercurial/hgsetup/config.py b/tools/mercurial/hgsetup/config.py
index 2a18ed50dacd..b5b20ef50d2e 100644
--- a/tools/mercurial/hgsetup/config.py
+++ b/tools/mercurial/hgsetup/config.py
@@ -17,8 +17,12 @@ class MercurialConfig(object):
     def __init__(self, infile=None):
         """Create a new instance, optionally from an existing hgrc file."""
 
+        # write_empty_values is necessary to prevent built-in extensions (which
+        # have no value) from being dropped on write.
+        # list_values aren't needed by Mercurial and disabling them prevents
+        # quotes from being added.
         self._c = ConfigObj(infile=infile, encoding='utf-8',
-            write_empty_values=True)
+            write_empty_values=True, list_values=False)
 
     @property
     def config(self):