diff --git a/.gitignore b/.gitignore
index 3c21249..2b6aed4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -147,3 +147,6 @@ yarn.lock
 # editor files
 .vscode
 .idea
+
+#tap files
+.tap/
diff --git a/index.js b/index.js
index 7a5a01f..3e97bde 100644
--- a/index.js
+++ b/index.js
@@ -2,10 +2,11 @@
 
 const fp = require('fastify-plugin')
 const Ajv = require('ajv')
+const AjvCore = require('ajv/dist/core')
 
 function fastifyResponseValidation (fastify, opts, next) {
   let ajv
-  if (opts.ajv && opts.ajv instanceof Ajv) {
+  if (opts.ajv && opts.ajv instanceof AjvCore.default) {
     ajv = opts.ajv
   } else {
     const { plugins: ajvPlugins, ...ajvOptions } = Object.assign({
diff --git a/package.json b/package.json
index b5db3f2..77173d0 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@fastify/response-validation",
-  "version": "2.5.1",
+  "version": "2.6.0",
   "description": "A simple plugin that enables response validation for Fastify.",
   "main": "index.js",
   "type": "commonjs",
@@ -16,7 +16,7 @@
     "fastify": "^4.2.1",
     "standard": "^17.0.0",
     "tap": "^16.3.0",
-    "tsd": "^0.29.0"
+    "tsd": "^0.30.1"
   },
   "scripts": {
     "lint": "standard",
diff --git a/test/ajv.test.js b/test/ajv.test.js
index a6f252f..c0d61e9 100644
--- a/test/ajv.test.js
+++ b/test/ajv.test.js
@@ -4,6 +4,8 @@ const test = require('tap').test
 const Fastify = require('fastify')
 const plugin = require('..')
 const Ajv = require('ajv')
+const Ajv2019 = require('ajv/dist/2019')
+const Ajv2020 = require('ajv/dist/2020')
 const ajvFormats = require('ajv-formats')
 const ajvErrors = require('ajv-errors')
 
@@ -171,6 +173,144 @@ test('use ajv errors with Ajv instance', async t => {
   t.equal(response.json().message, 'response should be an object with an integer property answer only')
 })
 
+test('use ajv formats with 2019 Ajv instance', async t => {
+  const fastify = Fastify()
+  const ajv = new Ajv2019()
+  ajvFormats(ajv)
+  await fastify.register(plugin, { ajv })
+
+  fastify.route({
+    method: 'GET',
+    url: '/',
+    schema: {
+      response: {
+        '2xx': {
+          type: 'object',
+          properties: {
+            answer: { type: 'number', format: 'float' }
+          }
+        }
+      }
+    },
+    handler: async (req, reply) => {
+      return { answer: 2.4 }
+    }
+  })
+
+  const response = await fastify.inject({
+    method: 'GET',
+    url: '/'
+  })
+
+  t.equal(response.statusCode, 200)
+  t.strictSame(JSON.parse(response.payload), { answer: 2.4 })
+})
+
+test('use ajv errors with 2019 Ajv instance', async t => {
+  const fastify = Fastify()
+  const ajv = new Ajv2019({ allErrors: true })
+  ajvErrors(ajv, { singleError: true })
+  await fastify.register(plugin, { ajv })
+
+  fastify.route({
+    method: 'GET',
+    url: '/',
+    schema: {
+      response: {
+        '2xx': {
+          type: 'object',
+          required: ['answer'],
+          properties: {
+            answer: { type: 'number' }
+          },
+          additionalProperties: false,
+          errorMessage: 'should be an object with an integer property answer only'
+        }
+      }
+    },
+    handler: async (req, reply) => {
+      return { notAnAnswer: 24 }
+    }
+  })
+
+  const response = await fastify.inject({
+    method: 'GET',
+    url: '/'
+  })
+
+  t.equal(response.statusCode, 500)
+  t.equal(response.json().message, 'response should be an object with an integer property answer only')
+})
+
+test('use ajv formats with 2020 Ajv instance', async t => {
+  const fastify = Fastify()
+  const ajv = new Ajv2020()
+  ajvFormats(ajv)
+  await fastify.register(plugin, { ajv })
+
+  fastify.route({
+    method: 'GET',
+    url: '/',
+    schema: {
+      response: {
+        '2xx': {
+          type: 'object',
+          properties: {
+            answer: { type: 'number', format: 'float' }
+          }
+        }
+      }
+    },
+    handler: async (req, reply) => {
+      return { answer: 2.4 }
+    }
+  })
+
+  const response = await fastify.inject({
+    method: 'GET',
+    url: '/'
+  })
+
+  t.equal(response.statusCode, 200)
+  t.strictSame(JSON.parse(response.payload), { answer: 2.4 })
+})
+
+test('use ajv errors with 2019 Ajv instance', async t => {
+  const fastify = Fastify()
+  const ajv = new Ajv2020({ allErrors: true })
+  ajvErrors(ajv, { singleError: true })
+  await fastify.register(plugin, { ajv })
+
+  fastify.route({
+    method: 'GET',
+    url: '/',
+    schema: {
+      response: {
+        '2xx': {
+          type: 'object',
+          required: ['answer'],
+          properties: {
+            answer: { type: 'number' }
+          },
+          additionalProperties: false,
+          errorMessage: 'should be an object with an integer property answer only'
+        }
+      }
+    },
+    handler: async (req, reply) => {
+      return { notAnAnswer: 24 }
+    }
+  })
+
+  const response = await fastify.inject({
+    method: 'GET',
+    url: '/'
+  })
+
+  t.equal(response.statusCode, 500)
+  t.equal(response.json().message, 'response should be an object with an integer property answer only')
+})
+
 test('should throw an error if ajv.plugins is not passed to instance and not array', async t => {
   t.plan(1)
   const fastify = Fastify()