diff --git a/requirements.txt b/requirements.txt
index 991646b4f..80801802e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,3 +3,4 @@ mkdocs-material==4.6.3
 mkdocs-minify-plugin==0.2.3
 pygments==2.6.1
 pymdown-extensions==7.0
+tornado>=6.3.3 # not directly required, pinned by Snyk to avoid a vulnerability