--- a/setup.py	Mon Apr 09 20:49:39 2018 +0900
+++ b/setup.py	Mon Apr 09 20:51:23 2018 +0900
@@ -878,9 +878,6 @@
                                        'mercurial/cext/bdiff.c'] + xdiff_srcs,
               include_dirs=common_include_dirs,
               depends=common_depends + ['mercurial/bdiff.h'] + xdiff_headers),
-    Extension('mercurial.cext.diffhelpers', ['mercurial/cext/diffhelpers.c'],
-              include_dirs=common_include_dirs,
-              depends=common_depends),
     Extension('mercurial.cext.mpatch', ['mercurial/mpatch.c',
                                         'mercurial/cext/mpatch.c'],
               include_dirs=common_include_dirs,