diff --git a/setup.py b/setup.py
index 43e44ad..5009736 100644
--- a/setup.py
+++ b/setup.py
@@ -33,7 +33,7 @@ setup(
     extras_require={
         "test": ["pytest", "black", "hypothesis"],
         "docs": ["sphinx_rtd_theme", "sphinx-autobuild"],
-        "mypy": ["mypy", "types-click", "types-tabulate"],
+        "mypy": ["mypy", "types-click", "types-tabulate", "types-python-dateutil"],
         "flake8": ["flake8"],
     },
     entry_points="""