diff --git a/requirements.txt b/requirements.txt
index 1bfe6b3..4a465c3 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,3 +7,4 @@ psutil
 pytest
 pytest-cov
 mock
+tornado>=6.5.3 # not directly required, pinned by Snyk to avoid a vulnerability