diff --git a/docs/requirements.txt b/docs/requirements.txt
index 8dcf7438..ac130cfd 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -5,3 +5,4 @@ sphinx-rtd-dark-mode
 sphinx_copybutton
 sphinx-autobuild
 tgcrypto
+tornado>=6.3.2 # not directly required, pinned by Snyk to avoid a vulnerability