diff --git a/conf.py b/conf.py
index 1dde709d75..f71e09adc1 100644
--- a/conf.py
+++ b/conf.py
@@ -357,4 +357,4 @@ intersphinx_mapping = {"cpython": ('https://docs.python.org/3/', None),
                        "register": ('https://circuitpython.readthedocs.io/projects/register/en/latest/', None)}
 
 def setup(app):
-    app.add_stylesheet("customstyle.css")
+    app.add_css_file("customstyle.css")