diff -r 0ae287eb6a4f -r e2796f193f06 mercurial/patch.py
--- a/mercurial/patch.py	Sat Jan 07 20:47:57 2017 -0800
+++ b/mercurial/patch.py	Mon Jan 09 10:51:44 2017 -0800
@@ -2169,6 +2169,11 @@
     if git:
         buildopts['git'] = get('git')
 
+        # since this is in the experimental section, we need to call
+        # ui.configbool directory
+        buildopts['showsimilarity'] = ui.configbool('experimental',
+                                                    'extendedheader.similarity')
+
         # need to inspect the ui object instead of using get() since we want to
         # test for an int
         hconf = ui.config('experimental', 'extendedheader.index')