diff --git a/requirements.txt b/requirements.txt
index aad9a34..455af8f 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -10,3 +10,4 @@ ipython>=7.17.0
 pyyaml>=6.0.0
 Jinja2>=3.1.0
 jupyter-bokeh>=3.0.7
+tornado>=6.3.2 # not directly required, pinned by Snyk to avoid a vulnerability