diff --git a/.travis.yml b/.travis.yml
index 0a5ead6..f98fed0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,5 @@
 language: node_js
 node_js:
+  - '12'
   - '10'
   - '8'
-  - '6'
-  - '4'
diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..a842e4c
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,6 @@
+import {ReadonlyDeep} from 'type-fest';
+import globalsJson = require('./globals.json');
+
+declare const globals: ReadonlyDeep<typeof globalsJson>;
+
+export = globals;
diff --git a/index.test-d.ts b/index.test-d.ts
new file mode 100644
index 0000000..4cd2356
--- /dev/null
+++ b/index.test-d.ts
@@ -0,0 +1,7 @@
+import {expectType, expectError} from 'tsd';
+import {ReadonlyDeep} from 'type-fest';
+import globals = require('.');
+
+expectType<ReadonlyDeep<{[key: string]: {[key: string]: boolean}}>>(globals);
+expectType<boolean>(globals.builtin.Array);
+expectError((globals.builtin.Array = true));
diff --git a/package.json b/package.json
index dfe459b..88b548d 100644
--- a/package.json
+++ b/package.json
@@ -10,7 +10,7 @@
 		"url": "sindresorhus.com"
 	},
 	"engines": {
-		"node": ">=4"
+		"node": ">=8"
 	},
 	"scripts": {
 		"test": "xo && ava"
@@ -29,13 +29,22 @@
 		"eslint",
 		"environments"
 	],
+	"dependencies": {
+		"type-fest": "^0.6.0"
+	},
 	"devDependencies": {
-		"ava": "0.21.0",
-		"xo": "0.18.0"
+		"ava": "^2.2.0",
+		"tsd": "^0.7.2",
+		"xo": "^0.24.0"
 	},
 	"xo": {
 		"ignores": [
 			"get-browser-globals.js"
 		]
+	},
+	"tsd": {
+		"compilerOptions": {
+			"resolveJsonModule": true
+		}
 	}
 }