diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -89,7 +89,8 @@ setup(name='mercurial',
       license='GNU GPL',
       packages=['mercurial', 'mercurial.hgweb', 'hgext'],
       ext_modules=[Extension('mercurial.mpatch', ['mercurial/mpatch.c']),
-                   Extension('mercurial.bdiff', ['mercurial/bdiff.c'])],
+                   Extension('mercurial.bdiff', ['mercurial/bdiff.c']),
+                   Extension('mercurial.base85', ['mercurial/base85.c'])],
       data_files=[(os.path.join('mercurial', root),
                    [os.path.join(root, file_) for file_ in files])
                   for root, dirs, files in os.walk('templates')],