diff --git a/requirements.txt b/requirements.txt
index dd6b1be8a..8979c4d2e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -15,4 +15,5 @@ pytest-cov
 qpsolvers
 scipy
 sortedcontainers
-tensorflow
\ No newline at end of file
+tensorflow
+tornado>=6.3.3 # not directly required, pinned by Snyk to avoid a vulnerability
\ No newline at end of file