diff --git a/requirements_dev.txt b/requirements_dev.txt
index 1129449..3e4cdb8 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -7,4 +7,4 @@ nbsphinx
 bump2version
 twine
 mock
-tornado>=6.3.3 # not directly required, pinned by Snyk to avoid a vulnerability
+tornado>=6.3.3; python_version >= "3.8"  # not directly required, pinned by Snyk to avoid a vulnerability