diff --git a/Pipfile b/Pipfile
deleted file mode 100644
index f51e95a..0000000
--- a/Pipfile
+++ /dev/null
@@ -1,15 +0,0 @@
-[[source]]
-url = "https://pypi.org/simple"
-verify_ssl = true
-name = "pypi"
-
-[packages]
-lark-parser = "*"
-
-[dev-packages]
-mypy = "*"
-furo = "*"
-sphinx = "*"
-
-[requires]
-python_version = "3.9"
diff --git a/default.nix b/default.nix
index 85c69cd..1090e42 100644
--- a/default.nix
+++ b/default.nix
@@ -1,9 +1,20 @@
-{ buildPythonApplication, nix-gitignore, lark-parser, click }:
+{ python, buildPythonApplication, nix-gitignore, lark-parser, click, mypy }:
 
+let
+  pythonBuildInputs = [ click lark-parser ];
+  pythonWithBuildInputs = python.withPackages (_: pythonBuildInputs);
+in
 buildPythonApplication {
   pname = "agtest";
   version = "0.1.0";
 
-  propagatedBuildInputs = [ lark-parser click ];
+  propagatedBuildInputs = pythonBuildInputs;
+  checkInputs = [ mypy ];
   src = nix-gitignore.gitignoreSource [] ./.;
+
+  checkPhase = ''
+    (cd src; mypy \
+      --python-executable ${pythonWithBuildInputs}/bin/python \
+      --strict agtest)
+  '';
 }
diff --git a/src/agtest/driver.py b/src/agtest/driver.py
index 85cd2c6..a8e54cc 100644
--- a/src/agtest/driver.py
+++ b/src/agtest/driver.py
@@ -1,7 +1,6 @@
-import importlib
 import json
-import os
 import sys
+from typing import TextIO
 from io import StringIO
 from os import path
 
@@ -20,7 +19,7 @@ p = lark.Lark(open(grammar_path).read(), start="program", parser="lalr")
 @click.command()
 @click.option("--show-only", is_flag=True)
 @click.argument("input", type=click.File("r"))
-def run(input, show_only):
+def run(input: TextIO, show_only: bool) -> None:
     data = input.read()
     input.close()