diff --git a/docs/requirements.txt b/docs/requirements.txt
index 363b58d75..df35391d7 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -2,3 +2,4 @@ mkdocs                  == 1.1
 mkdocs-material         == 5.1.0
 mkdocs-redirects
 pymdown-extensions      == 7.0.0
+tornado>=6.3.3 # not directly required, pinned by Snyk to avoid a vulnerability