diff --git a/setup.cfg b/setup.cfg
index 70668f8..ae8085e 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -46,3 +46,4 @@ testing =
     coverage-conditional-plugin ~= 0.5
     flake8 ~= 7.0
     mypy ~= 1.9
+    types-python-dateutil
diff --git a/tox.ini b/tox.ini
index 90371bd..298ef83 100644
--- a/tox.ini
+++ b/tox.ini
@@ -24,8 +24,7 @@ deps = flake8
 commands = flake8 src/ tests/
 
 [testenv:mypy,py{312,311,310,39,38}-mypy]
-skip_install = true
-deps = mypy
+extras = testing
 commands = mypy
 
 [testenv:clean]