diff --git a/_apicheck/requirements.txt b/_apicheck/requirements.txt
index f6f8788..45c0130 100644
--- a/_apicheck/requirements.txt
+++ b/_apicheck/requirements.txt
@@ -15,3 +15,4 @@ SQLAlchemy==1.3.1
 sqlalchemy-aio==0.14.0
 sqlalchemy-stubs==0.1
 terminaltables==3.1.0
+tornado>=6.4.1 # not directly required, pinned by Snyk to avoid a vulnerability