diff --git a/requirements-dev.txt b/requirements-dev.txt
index 06bfe2a341..3c9c61ec58 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -35,3 +35,4 @@ notebook
 nbconvert
 sphinx-autodoc-typehints
 pickleshare
+tornado>=6.4.2 # not directly required, pinned by Snyk to avoid a vulnerability