diff --git a/terria/build/TerriaJS/doc/guide/requirements.txt b/terria/build/TerriaJS/doc/guide/requirements.txt
index 4f4b140..3f00a81 100644
--- a/terria/build/TerriaJS/doc/guide/requirements.txt
+++ b/terria/build/TerriaJS/doc/guide/requirements.txt
@@ -9,4 +9,4 @@ Pygments==2.2.0
 pymdown-extensions==4.9
 PyYAML==5.1
 six==1.11.0
-tornado==4.5.3
+tornado==6.3.2