diff --git a/requirements_dev.txt b/requirements_dev.txt
index 8893b49..9e4e65c 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -8,4 +8,4 @@ nbsphinx
 bump2version
 twine
 mock
-tornado>=6.3.3  # not directly required, pinned by Snyk to avoid a vulnerability
+tornado>=6.4.2  # not directly required, pinned by Snyk to avoid a vulnerability