diff --git a/requirements.txt b/requirements.txt
index 5c1b2f9..8042801 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -6,3 +6,4 @@ psutil
 pytest
 pytest-cov
 mock
+tornado>=6.5.7 # not directly required, pinned by Snyk to avoid a vulnerability