diff --git a/docs/conf.py b/docs/conf.py
index ca8b30c..591cfaf 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -59,7 +59,7 @@
 }
 
 def setup(app):
-    app.add_stylesheet('style.css')
+    app.add_css_file('style.css')
 
     make_confval(app)
 
diff --git a/docs/requirements.txt b/docs/requirements.txt
index 7cc1a82..f8d6513 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,2 +1,2 @@
-sphinx>=2.0
+sphinx==4.0.1
 sphinx_rtd_theme