diff --git a/pyproject.toml b/pyproject.toml
index 64912b43..a47ecf74 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -54,3 +54,4 @@ addopts = [
 check_untyped_defs = true
 disallow_incomplete_defs = true
 disallow_untyped_decorators = true
+disallow_untyped_defs = true