diff --git a/Documentation/sphinx/requirements.txt b/Documentation/sphinx/requirements.txt
index 489f6626de67..5030d346d23b 100644
--- a/Documentation/sphinx/requirements.txt
+++ b/Documentation/sphinx/requirements.txt
@@ -1,3 +1,4 @@
 docutils
 Sphinx==2.4.4
 sphinx_rtd_theme
+six