diff --git a/docs/requirements.txt b/docs/requirements.txt
index 44af373ac2..8bec8368c7 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -2,3 +2,4 @@
 
 # use md instead of rst
 recommonmark
+sphinx>=3.0.4 # not directly required, pinned by Snyk to avoid a vulnerability