diff --git a/requirements.txt b/requirements.txt
index dda37b6..bbd6192 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
-sphinx>=3.5.4
+sphinx<=4.0.3
 numpydoc>=1.1.0
 recommonmark>=0.7.1
 jupyter_sphinx>=0.3.2