diff --git a/README.md b/README.md
index 40e609d..0716903 100644
--- a/README.md
+++ b/README.md
@@ -50,6 +50,10 @@ fastify.listen({ port: 3000 }, err => {
 `@fastify/helmet` is a wrapper around `helmet` that adds an `'onRequest'` hook
 and a `reply.helmet` decorator.
 
+TypeScript note: after `fastify.register(helmet)`, `reply.helmet()` and
+`reply.cspNonce` are inferred from that registered instance. The `helmet`
+route option still uses Fastify route option augmentation.
+
 It accepts the same options as `helmet`. See [helmet documentation](https://helmetjs.github.io/).
 
 ### Apply Helmet to all routes
diff --git a/package.json b/package.json
index 6a68f84..5a09bac 100644
--- a/package.json
+++ b/package.json
@@ -65,7 +65,7 @@
     "@types/node": "^25.0.3",
     "c8": "^11.0.0",
     "eslint": "^9.17.0",
-    "fastify": "^5.0.0",
+    "fastify": "github:fastify/fastify#feat/typed-decorators",
     "neostandard": "^0.12.0",
     "tsd": "^0.33.0"
   },
diff --git a/types/index.d.ts b/types/index.d.ts
index 2920830..3c78121 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -1,4 +1,11 @@
-import { FastifyPluginAsync, RawServerBase, RawServerDefault } from 'fastify'
+import {
+  AnyFastifyInstance,
+  ApplyDecorators,
+  FastifyPluginAsync,
+  RawServerBase,
+  RawServerDefault,
+  UnEncapsulatedPlugin
+} from 'fastify'
 import helmet, { contentSecurityPolicy, HelmetOptions } from 'helmet'
 
 declare module 'fastify' {
@@ -7,22 +14,29 @@ declare module 'fastify' {
     RawServer extends RawServerBase = RawServerDefault
   > extends fastifyHelmet.FastifyHelmetRouteOptions { }
 
-  interface FastifyReply {
-    cspNonce: {
-      script: string;
-      style: string;
-    },
-    helmet: (opts?: HelmetOptions) => typeof helmet
-  }
-
   export interface RouteOptions extends fastifyHelmet.FastifyHelmetRouteOptions { }
 }
 
-type FastifyHelmet = FastifyPluginAsync<fastifyHelmet.FastifyHelmetOptions> & {
-  contentSecurityPolicy: typeof contentSecurityPolicy;
-}
-
 declare namespace fastifyHelmet {
+  export type FastifyHelmetPluginDecorators = {
+    reply: {
+      cspNonce: {
+        script: string;
+        style: string;
+      };
+      helmet: (opts?: HelmetOptions) => typeof helmet;
+    }
+  }
+
+  export type FastifyHelmetPlugin<TInstance extends AnyFastifyInstance = AnyFastifyInstance> = UnEncapsulatedPlugin<
+    FastifyPluginAsync<
+      fastifyHelmet.FastifyHelmetOptions,
+      TInstance,
+      ApplyDecorators<TInstance, FastifyHelmetPluginDecorators>
+    >
+  > & {
+    contentSecurityPolicy: typeof contentSecurityPolicy;
+  }
 
   export interface FastifyHelmetRouteOptions {
     helmet?: Omit<FastifyHelmetOptions, 'global'> | false;
@@ -33,9 +47,9 @@ declare namespace fastifyHelmet {
     global?: boolean;
   } & NonNullable<HelmetOptions>
 
-  export const fastifyHelmet: FastifyHelmet
+  export const fastifyHelmet: FastifyHelmetPlugin
   export { fastifyHelmet as default }
 }
 
-declare function fastifyHelmet (...params: Parameters<FastifyHelmet>): ReturnType<FastifyHelmet>
+declare function fastifyHelmet (...params: Parameters<fastifyHelmet.FastifyHelmetPlugin>): ReturnType<fastifyHelmet.FastifyHelmetPlugin>
 export = fastifyHelmet
diff --git a/types/index.test-d.ts b/types/index.test-d.ts
index aa9a6ca..a35e3c9 100644
--- a/types/index.test-d.ts
+++ b/types/index.test-d.ts
@@ -1,19 +1,21 @@
-import fastify, { FastifyPluginAsync } from 'fastify'
+import fastify from 'fastify'
 import helmet from 'helmet'
 import { expectAssignable, expectError, expectType } from 'tsd'
-import fastifyHelmet, { FastifyHelmetOptions, FastifyHelmetRouteOptions } from '..'
+import fastifyHelmet, {
+  FastifyHelmetOptions,
+  FastifyHelmetPlugin,
+  FastifyHelmetPluginDecorators,
+  FastifyHelmetRouteOptions
+} from '..'
 
 // Plugin registered with no options
-const appOne = fastify()
-appOne.register(fastifyHelmet)
+const appOne = fastify().register(fastifyHelmet)
 
 // Plugin registered with an empty object option
-const appTwo = fastify()
 expectAssignable<FastifyHelmetOptions>({})
-appTwo.register(fastifyHelmet, {})
+const appTwo = fastify().register(fastifyHelmet, {})
 
 // Plugin registered with all helmet middlewares disabled
-const appThree = fastify()
 const helmetOptions = {
   contentSecurityPolicy: false,
   dnsPrefetchControl: false,
@@ -27,11 +29,10 @@ const helmetOptions = {
   xssFilter: false
 }
 expectAssignable<FastifyHelmetOptions>(helmetOptions)
-appThree.register(fastifyHelmet, helmetOptions)
+const appThree = fastify().register(fastifyHelmet, helmetOptions)
 
 // Plugin registered with helmet middlewares custom settings
-const appFour = fastify()
-appFour.register(fastifyHelmet, {
+const appFour = fastify().register(fastifyHelmet, {
   contentSecurityPolicy: {
     directives: {
       'directive-1': ['foo', 'bar']
@@ -64,19 +65,14 @@ appFour.register(fastifyHelmet, {
 })
 
 // Plugin registered with `enableCSPNonces` option and helmet default CSP settings
-const appFive = fastify()
-appFive.register(fastifyHelmet, { enableCSPNonces: true })
+const appFive = fastify().register(fastifyHelmet, { enableCSPNonces: true })
 
 appFive.get('/', function (_request, reply) {
-  expectType<{
-    script: string;
-    style: string;
-  }>(reply.cspNonce)
+  expectType<FastifyHelmetPluginDecorators['reply']['cspNonce']>(reply.cspNonce)
 })
 
 // Plugin registered with `enableCSPNonces` option and custom CSP settings
-const appSix = fastify()
-appSix.register(fastifyHelmet, {
+const appSix = fastify().register(fastifyHelmet, {
   enableCSPNonces: true,
   contentSecurityPolicy: {
     directives: {
@@ -87,20 +83,17 @@ appSix.register(fastifyHelmet, {
 })
 
 appSix.get('/', function (_request, reply) {
-  expectType<{
-    script: string;
-    style: string;
-  }>(reply.cspNonce)
+  expectType<FastifyHelmetPluginDecorators['reply']['cspNonce']>(reply.cspNonce)
 })
 
 const csp = fastifyHelmet.contentSecurityPolicy
 expectType<typeof helmet.contentSecurityPolicy>(csp)
 
 // Plugin registered with `global` set to `true`
-const appSeven = fastify()
-appSeven.register(fastifyHelmet, { global: true })
+const appSeven = fastify().register(fastifyHelmet, { global: true })
 
 appSeven.get('/route-with-disabled-helmet', { helmet: false }, function (_request, reply) {
+  expectType<FastifyHelmetPluginDecorators['reply']['helmet']>(reply.helmet)
   expectType<typeof helmet>(reply.helmet())
 })
 
@@ -113,8 +106,7 @@ expectError(
 )
 
 // Plugin registered with `global` set to `false`
-const appEight = fastify()
-appEight.register(fastifyHelmet, { global: false })
+const appEight = fastify().register(fastifyHelmet, { global: false })
 
 appEight.get('/disabled-helmet', function (_request, reply) {
   expectType<typeof helmet>(reply.helmet(helmetOptions))
@@ -152,20 +144,14 @@ expectAssignable<FastifyHelmetRouteOptions>(routeHelmetOptions)
 
 appEight.get('/enabled-helmet', routeHelmetOptions, function (_request, reply) {
   expectType<typeof helmet>(reply.helmet())
-  expectType<{
-    script: string;
-    style: string;
-  }>(reply.cspNonce)
+  expectType<FastifyHelmetPluginDecorators['reply']['cspNonce']>(reply.cspNonce)
 })
 
 appEight.get('/enable-framegard', {
   helmet: { frameguard: true }
 }, function (_request, reply) {
   expectType<typeof helmet>(reply.helmet())
-  expectType<{
-    script: string;
-    style: string;
-  }>(reply.cspNonce)
+  expectType<FastifyHelmetPluginDecorators['reply']['cspNonce']>(reply.cspNonce)
 })
 
 // Plugin registered with an invalid helmet option
@@ -176,9 +162,8 @@ expectError(
   })
 )
 
-// fastify-helmet instance is using the FastifyHelmetOptions options
-expectType<
-  FastifyPluginAsync<FastifyHelmetOptions> & {
-    contentSecurityPolicy: typeof helmet.contentSecurityPolicy;
-  }
->(fastifyHelmet)
+expectType<FastifyHelmetPlugin>(fastifyHelmet)
+expectType<typeof appOne>(appOne)
+expectType<typeof appTwo>(appTwo)
+expectType<typeof appThree>(appThree)
+expectType<typeof appFour>(appFour)