diff --git a/approval_utilities/py.typed b/approval_utilities/py.typed
new file mode 100644
index 0000000..e69de29
diff --git a/approvaltests/py.typed b/approvaltests/py.typed
new file mode 100644
index 0000000..e69de29
diff --git a/requirements.dev.txt b/requirements.dev.txt
index 7ca42ea..9cfe502 100644
--- a/requirements.dev.txt
+++ b/requirements.dev.txt
@@ -1,3 +1,5 @@
 -r requirements.prod.txt
 -r requirements.test.txt
-black
\ No newline at end of file
+black
+setuptools
+mypy
diff --git a/run_tests.sh b/run_tests.sh
index 311585e..49d92d8 100755
--- a/run_tests.sh
+++ b/run_tests.sh
@@ -2,4 +2,5 @@
 set -euo pipefail
 
 python3 -m pip --disable-pip-version-check install tox
-tox -e py
\ No newline at end of file
+tox -e py
+tox -e test__py_typed_files_exist
diff --git a/test__py_typed_files_exist.py b/test__py_typed_files_exist.py
new file mode 100644
index 0000000..8eb26b4
--- /dev/null
+++ b/test__py_typed_files_exist.py
@@ -0,0 +1,59 @@
+import pathlib
+import tempfile
+import subprocess
+import sys
+import time
+import typing
+
+from version import version_number
+
+
+def main() -> None:
+    for package_name, setup_file in [
+        ("approval_utilities", "setup.approval_utilities.py"),
+        ("approvaltests", "setup.py"),
+    ]:
+        build_number = str(int(time.time()))
+        _run_python_checked(
+            [
+                setup_file,
+                "bdist_wheel",
+                "--build-number",
+                build_number,
+            ]
+        )
+        _run_python_checked(
+            [
+                "-m",
+                "pip",
+                "install",
+                "--force-reinstall",
+                # version_number starts with `v`; remove that character
+                f"dist/{package_name}-{version_number[1:]}-{build_number}-py3-none-any.whl",
+            ]
+        )
+
+        with tempfile.NamedTemporaryFile(suffix=".py") as _test_file:
+            test_file = pathlib.Path(_test_file.name)
+            test_file.write_text(
+                f"import {package_name}"
+            )
+
+            _run_python_checked(
+                ["-m", "mypy", test_file.name],
+                cwd=test_file.parent,
+            )
+
+
+def _run_python_checked(
+    args: typing.List[str], cwd: typing.Optional[pathlib.Path] = None
+) -> None:
+    subprocess.run(
+        [sys.executable, *args],
+        check=True,
+        cwd=cwd,
+    )
+
+
+if __name__ == "__main__":
+    main()
diff --git a/tox.ini b/tox.ini
index 7aa41cd..a2cb4c6 100644
--- a/tox.ini
+++ b/tox.ini
@@ -25,3 +25,7 @@ commands =
     ; automatically install hook at .git/hooks
     ;{envdir}/bin/pre-commit install
 
+[testenv:test__py_typed_files_exist]
+deps = -rrequirements.txt
+commands =
+    python test__py_typed_files_exist.py