diff --git a/requirements-doc.txt b/requirements-doc.txt
index 588a94fda..c6d6091fe 100644
--- a/requirements-doc.txt
+++ b/requirements-doc.txt
@@ -14,4 +14,5 @@ yarl==1.8.1
 frozenlist==1.3.1
 mkdocs-minify-plugin
 mkdocs-rss-plugin
-pytest-examples
\ No newline at end of file
+pytest-examples
+tornado>=6.4.2 # not directly required, pinned by Snyk to avoid a vulnerability
\ No newline at end of file