diff --git a/requirements/integration.txt b/requirements/integration.txt
index 4d88e83..bbc5ed2 100644
--- a/requirements/integration.txt
+++ b/requirements/integration.txt
@@ -36,6 +36,7 @@ twine
 md-toc
 straitjacket
 pycalver
+lib3to6
 
 # needed for mypy coverage report
 lxml