--- a/mercurial/patch.py	Mon Jan 09 11:24:18 2017 -0800
+++ b/mercurial/patch.py	Mon Jan 09 11:01:45 2017 -0800
@@ -2350,6 +2350,7 @@
                     ('new', 'diff.extended'),
                     ('deleted', 'diff.extended'),
                     ('index', 'diff.extended'),
+                    ('similarity', 'diff.extended'),
                     ('---', 'diff.file_a'),
                     ('+++', 'diff.file_b')]
     textprefixes = [('@', 'diff.hunk'),