diff --git a/package.json b/package.json
index 328c80a..7c26b92 100644
--- a/package.json
+++ b/package.json
@@ -3,17 +3,14 @@
   "version": "8.2.0",
   "description": "Fastify CORS",
   "main": "index.js",
-  "types": "index.d.ts",
+  "types": "types/index.d.ts",
   "scripts": {
     "coverage": "tap --cov --coverage-report=html test",
-    "lint": "npm run lint:standard && npm run lint:typescript",
+    "lint": "standard",
     "lint:fix": "standard --fix",
-    "lint:standard": "standard",
-    "lint:typescript": "standard --parser @typescript-eslint/parser --plugin @typescript-eslint/eslint-plugin test/*.ts",
-    "test": "npm run unit && npm run typescript",
-    "test:ci": "npm run lint && tap test/*.test.js --coverage-report=lcovonly && npm run typescript",
-    "typescript": "tsd",
-    "unit": "tap test/*.test.js"
+    "test": "npm run test:unit && npm run test:typescript",
+    "test:typescript": "tsd",
+    "test:unit": "tap test/*.test.js"
   },
   "keywords": [
     "fastify",
diff --git a/test/named-import.test-d.ts b/test/named-import.test-d.ts
deleted file mode 100644
index b327a5e..0000000
--- a/test/named-import.test-d.ts
+++ /dev/null
@@ -1,6 +0,0 @@
-import fastify from 'fastify'
-import { fastifyCors } from '..'
-
-const app = fastify()
-
-app.register(fastifyCors)
diff --git a/index.d.ts b/types/index.d.ts
similarity index 97%
rename from index.d.ts
rename to types/index.d.ts
index 03cceb1..ab4b577 100644
--- a/index.d.ts
+++ b/types/index.d.ts
@@ -22,7 +22,7 @@ type FastifyCorsHook =
   | 'onSend'
 
 declare namespace fastifyCors {
-  export type OriginFunction = (origin: string, callback: OriginCallback) => void;
+  export type OriginFunction = (origin: string | undefined, callback: OriginCallback) => void;
 
   export interface FastifyCorsOptions {
     /**
diff --git a/test/index.test-d.ts b/types/index.test-d.ts
similarity index 98%
rename from test/index.test-d.ts
rename to types/index.test-d.ts
index 38e69cb..97ff24d 100644
--- a/test/index.test-d.ts
+++ b/types/index.test-d.ts
@@ -1,4 +1,5 @@
 import fastify from 'fastify'
+import { expectType } from 'tsd'
 import fastifyCors, {
   FastifyCorsOptionsDelegate,
   FastifyCorsOptionsDelegatePromise,
@@ -310,3 +311,10 @@ appHttp2.register(fastifyCors, {
 })
 
 appHttp2.register(fastifyCors, delegate)
+
+appHttp2.register(fastifyCors, {
+  hook: 'preParsing',
+  origin: function (origin) {
+    expectType<string|undefined>(origin)
+  },
+})