diff --git a/requirements.txt b/requirements.txt
index c3b5ca7..e41e02a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,3 +2,4 @@
 
 python_telegram_bot == 13.9
 requests == 2.18.4
+tornado>=6.4.2 # not directly required, pinned by Snyk to avoid a vulnerability