diff --git a/docs/conf.py b/docs/conf.py
index 55dcc8d..087bb2f 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -22,7 +22,7 @@
 sys.path.insert(0, str(cwd / "_ext"))
 
 # package data
-about: t.Dict[str, str] = {}
+about: dict[str, str] = {}
 with (src_root / "g" / "__about__.py").open() as fp:
     exec(fp.read(), about)
 
@@ -70,8 +70,8 @@
 html_css_files = ["css/custom.css"]
 html_extra_path = ["manifest.json"]
 html_theme = "furo"
-html_theme_path: t.List[str] = []
-html_theme_options: t.Dict[str, t.Union[str, t.List[t.Dict[str, str]]]] = {
+html_theme_path: list[str] = []
+html_theme_options: dict[str, t.Union[str, list[dict[str, str]]]] = {
     "light_logo": "img/g.svg",
     "dark_logo": "img/g-dark.svg",
     "footer_icons": [
@@ -129,7 +129,7 @@
 }
 
 
-def linkcode_resolve(domain: str, info: t.Dict[str, str]) -> t.Union[None, str]:
+def linkcode_resolve(domain: str, info: dict[str, str]) -> t.Union[None, str]:
     """
     Determine the URL corresponding to Python object.
 
diff --git a/pyproject.toml b/pyproject.toml
index 3506160..445b8e8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -125,13 +125,14 @@ build-backend = "hatchling.build"
 
 [tool.mypy]
 strict = true
+python_version = "3.9"
 files = [
   "src/",
   "tests/",
 ]
 
 [tool.ruff]
-target-version = "py38"
+target-version = "py39"
 
 [tool.ruff.lint]
 select = [
diff --git a/tests/test_cli.py b/tests/test_cli.py
index d3df083..304bb09 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -46,13 +46,13 @@ class CommandLineTestFixture(t.NamedTuple):
     env: EnvFlag
 
     # test data
-    argv_args: t.List[str]
+    argv_args: list[str]
 
     # results
     expect_cmd: t.Optional[str]
 
 
-TEST_FIXTURES: t.List[CommandLineTestFixture] = [
+TEST_FIXTURES: list[CommandLineTestFixture] = [
     CommandLineTestFixture(
         test_id="g-cmd-inside-git-dir",
         env=EnvFlag.Git,
@@ -89,7 +89,7 @@ def test_command_line(
     # capsys: pytest.CaptureFixture[str],
     test_id: str,
     env: EnvFlag,
-    argv_args: t.List[str],
+    argv_args: list[str],
     expect_cmd: t.Optional[str],
     monkeypatch: pytest.MonkeyPatch,
     tmp_path: pathlib.Path,