diff --git a/README.md b/README.md
index 128f83c..32c2224 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,7 @@ When you build plugins for Fastify and you want that them to be accessible in th
 1. Use the `skip-override` hidden property
 2. Use this module
 
+__Note: the v4.x series of this module covers Fastify v4__
 __Note: the v2.x & v3.x series of this module covers Fastify v3. For Fastify v2 support, refer to the v1.x series.__
 
 ## Usage
@@ -50,7 +51,7 @@ const fp = require('fastify-plugin')
 module.exports = fp(function (fastify, opts, next) {
   // your plugin code
   next()
-}, { fastify: '3.x' })
+}, { fastify: '4.x' })
 ```
 
 If you need to check the Fastify version only, you can pass just the version string.
@@ -69,7 +70,7 @@ function plugin (fastify, opts, next) {
 }
 
 module.exports = fp(plugin, {
-  fastify: '3.x',
+  fastify: '4.x',
   name: 'your-plugin-name'
 })
 ```
@@ -86,7 +87,7 @@ function plugin (fastify, opts, next) {
 }
 
 module.exports = fp(plugin, {
-  fastify: '3.x',
+  fastify: '4.x',
   decorators: {
     fastify: ['plugin1', 'plugin2'],
     reply: ['compress']
diff --git a/package.json b/package.json
index 1f239d7..4de0a1a 100644
--- a/package.json
+++ b/package.json
@@ -26,7 +26,7 @@
   "homepage": "https://github.com/fastify/fastify-plugin#readme",
   "devDependencies": {
     "@types/node": "^17.0.0",
-    "fastify": "^3.3.0",
+    "fastify": "^4.0.1",
     "proxyquire": "^2.1.3",
     "standard": "^17.0.0",
     "tap": "^16.0.1",
diff --git a/test/bundlers.test.js b/test/bundlers.test.js
index 7ae9e39..a48ff5b 100644
--- a/test/bundlers.test.js
+++ b/test/bundlers.test.js
@@ -20,7 +20,7 @@ test('webpack removes require.main.filename', (t) => {
   fp((fastify, opts, next) => {
     next()
   }, {
-    fastify: '^3.0.0'
+    fastify: '^4.0.0'
   })
 
   t.end()
diff --git a/test/checkVersion.test.js b/test/checkVersion.test.js
index 3989cf3..f64a8fa 100644
--- a/test/checkVersion.test.js
+++ b/test/checkVersion.test.js
@@ -17,7 +17,7 @@ test('checkVersion having require.main.filename', (t) => {
   fp((fastify, opts, next) => {
     next()
   }, {
-    fastify: '^3.0.0'
+    fastify: '^4.0.0'
   })
 
   t.end()
@@ -40,7 +40,7 @@ test('checkVersion having no require.main.filename but process.argv[1]', (t) =>
   fp((fastify, opts, next) => {
     next()
   }, {
-    fastify: '^3.0.0'
+    fastify: '^4.0.0'
   })
 
   t.end()
@@ -66,7 +66,7 @@ test('checkVersion having no require.main.filename and no process.argv[1]', (t)
   fp((fastify, opts, next) => {
     next()
   }, {
-    fastify: '^3.0.0'
+    fastify: '^4.0.0'
   })
 
   t.end()
diff --git a/test/test.js b/test/test.js
index 2d68d66..fc75588 100644
--- a/test/test.js
+++ b/test/test.js
@@ -183,12 +183,12 @@ test('should check fastify dependency graph - plugin', t => {
   const fastify = Fastify()
 
   fastify.register(fp((fastify, opts, next) => next(), {
-    fastify: '3.x',
+    fastify: '4.x',
     name: 'plugin1-name'
   }))
 
   fastify.register(fp((fastify, opts, next) => next(), {
-    fastify: '3.x',
+    fastify: '4.x',
     name: 'test',
     dependencies: ['plugin1-name', 'plugin2-name']
   }))
@@ -203,12 +203,12 @@ test('should check fastify dependency graph - decorate', t => {
   const fastify = Fastify()
 
   fastify.decorate('plugin1', fp((fastify, opts, next) => next(), {
-    fastify: '3.x',
+    fastify: '4.x',
     name: 'plugin1-name'
   }))
 
   fastify.register(fp((fastify, opts, next) => next(), {
-    fastify: '3.x',
+    fastify: '4.x',
     name: 'test',
     decorators: { fastify: ['plugin1', 'plugin2'] }
   }))
@@ -223,12 +223,12 @@ test('should check fastify dependency graph - decorateReply', t => {
   const fastify = Fastify()
 
   fastify.decorateReply('plugin1', fp((fastify, opts, next) => next(), {
-    fastify: '3.x',
+    fastify: '4.x',
     name: 'plugin1-name'
   }))
 
   fastify.register(fp((fastify, opts, next) => next(), {
-    fastify: '3.x',
+    fastify: '4.x',
     name: 'test',
     decorators: { reply: ['plugin1', 'plugin2'] }
   }))