diff --git a/tox.ini b/tox.ini
index 2b7e578..eb12a1a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -29,6 +29,7 @@ deps =
     setuptools-scm
     pytest
     pytest-cov
+    types-PyYAML
     flake8
     mypy
 setenv =