diff --git a/requirements.txt b/requirements.txt
index 077adb580..485d8c596 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,3 +4,4 @@ sphinx-autobuild==2021.3.14
 sphinx-inline-tabs==2023.4.21
 sphinx-copybutton==0.5.2
 sphinx-toolbox==3.5.0
+tornado>=6.4.2 # not directly required, pinned by Snyk to avoid a vulnerability