diff --git a/requirements.txt b/requirements.txt
index b860adc..5a02fa8 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,3 +3,4 @@ scikit-image
 scipy
 autopep8
 bash_kernel
+tornado>=6.3.3 # not directly required, pinned by Snyk to avoid a vulnerability