diff --git a/docs/requirements.txt b/docs/requirements.txt
index a46d792b391..fc044bb1a49 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,7 +1,7 @@
 -f http://simple.crate.io/
 MarkupSafe==0.23
 Pygments==2.0.2
-sphinx
+sphinx==3.4.3
 # temporarily disabled because of an issue on RTD. see also conf.py
 #sphinxcontrib-spelling
 pyenchant