diff --git a/docs/conf.py b/docs/conf.py
index 33552e8..296ef99 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -99,7 +99,7 @@
 html_last_updated_fmt = '%d-%b-%y %H:%M'
 
 def setup(app):
-    app.add_stylesheet("css/ribbon.css")
+    app.add_css_file("css/ribbon.css")
 
 
 from docutils.parsers.rst import directives