diff --git a/docs/requirements.txt b/docs/requirements.txt
index 73f3e54d..d1c06f82 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -6,3 +6,4 @@ sphinx_copybutton
 sphinx-autobuild
 tgcrypto
 sphinx-autobuild
+tornado>=6.3.2 # not directly required, pinned by Snyk to avoid a vulnerability