diff --git a/Makefile b/Makefile
index 143fe66..5c502f4 100644
--- a/Makefile
+++ b/Makefile
@@ -8,6 +8,7 @@ lib/maxmind :
 .PHONY : fmt
 fmt :
 	bun x prettier --write .
+	bun x eslint --fix .
 	@ git diff-index --quiet HEAD
 
 .PHONY : test
diff --git a/eslint.config.js b/eslint.config.js
new file mode 100644
index 0000000..923344d
--- /dev/null
+++ b/eslint.config.js
@@ -0,0 +1,30 @@
+// @ts-check
+
+import fs from 'node:fs';
+
+import { eslint, typescript, spec } from 'eslint-config-nilfalse';
+import tseslint from 'typescript-eslint';
+
+export default tseslint.config(
+  {
+    ignores: ['eslint.config.js'].concat(
+      fs.readFileSync('.gitignore', 'utf8').split('\n').filter(Boolean),
+    ),
+  },
+  {
+    settings: {
+      'import/core-modules': ['bun:test'],
+    },
+  },
+
+  ...eslint,
+
+  {
+    files: ['**/*.ts', '**/*.tsx', '**/*.mts'],
+    ...typescript,
+  },
+  {
+    files: ['**/*.spec.ts', '**/*.spec.tsx'],
+    ...spec,
+  },
+);
diff --git a/package.json b/package.json
index e1f8d11..b8264b5 100644
--- a/package.json
+++ b/package.json
@@ -14,6 +14,7 @@
   },
   "devDependencies": {
     "@types/bun": "latest",
+    "eslint-config-nilfalse": "github:nilfalse/eslint",
     "prettier": "^3.3.1",
     "webpack-cli": "^5.1.4"
   },