diff --git a/requirements-dev.txt b/requirements-dev.txt
index b82cf4ae11..1fc99dcc45 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -22,3 +22,4 @@ sphinx-immaterial
 sphinxcontrib-spelling
 sphinx_autodoc_typehints
 wheel
+tornado>=6.5 # not directly required, pinned by Snyk to avoid a vulnerability