diff --git a/docs/requirements.txt b/docs/requirements.txt
index f555907..89bddc4 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -4,3 +4,4 @@ sphinx
 sphinx-autobuild
 sphinx-click
 myst_parser
+tornado>=6.4.2 # not directly required, pinned by Snyk to avoid a vulnerability