diff --git a/docs/index.rst b/docs/index.rst
index ccecc89..431eb5f 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -9,6 +9,9 @@ project.
 
 .. _test coverage: https://buildbot.wuttaproject.org/coverage/wuttatell/
 
+.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
+   :target: https://github.com/psf/black
+
 
 .. toctree::
    :maxdepth: 2