diff --git a/lib/cookie.js b/lib/cookie.js
new file mode 100644
index 0000000..d157bd6
--- /dev/null
+++ b/lib/cookie.js
@@ -0,0 +1,67 @@
+'use strict'
+
+const isConnectionSecure = require('./isConnectionSecure')
+
+module.exports = class Cookie {
+  constructor (cookie, request) {
+    const originalMaxAge = cookie.originalMaxAge || cookie.maxAge || null
+    this.path = cookie.path || '/'
+    this.secure = cookie.secure ?? null
+    this.sameSite = cookie.sameSite || null
+    this.domain = cookie.domain || null
+    this.httpOnly = cookie.httpOnly !== undefined ? cookie.httpOnly : true
+    this._expires = null
+
+    if (originalMaxAge) {
+      this.maxAge = originalMaxAge
+    } else if (cookie.expires) {
+      this.expires = new Date(cookie.expires)
+      this.originalMaxAge = null
+    } else {
+      this.originalMaxAge = originalMaxAge
+    }
+
+    if (this.secure === 'auto') {
+      if (isConnectionSecure(request)) {
+        this.secure = true
+      } else {
+        this.sameSite = 'Lax'
+        this.secure = false
+      }
+    }
+  }
+
+  set expires (date) {
+    this._expires = date
+  }
+
+  get expires () {
+    return this._expires
+  }
+
+  set maxAge (ms) {
+    this.expires = new Date(Date.now() + ms)
+    // we force the same originalMaxAge to match old behavior
+    this.originalMaxAge = ms
+  }
+
+  get maxAge () {
+    if (this.expires instanceof Date) {
+      return this.expires.valueOf() - Date.now()
+    } else {
+      return null
+    }
+  }
+
+  toJSON () {
+    return {
+      expires: this._expires,
+      originalMaxAge: this.originalMaxAge,
+      sameSite: this.sameSite,
+      secure: this.secure,
+      path: this.path,
+      httpOnly: this.httpOnly,
+      domain: this.domain
+    }
+  }
+}
diff --git a/lib/fastifySession.js b/lib/fastifySession.js
index d546941..b34f6ce 100644
--- a/lib/fastifySession.js
+++ b/lib/fastifySession.js
@@ -184,7 +184,8 @@ function fastifySession (fastify, options, next) {
         reply.setCookie(
           cookieName,
           hasCookiePrefix ? `${cookiePrefix}${session.encryptedSessionId}` : session.encryptedSessionId,
-          session.cookie
+          // we need to remove extra properties to align the same with `express-session`
+          session.cookie.toJSON()
         )
         done()
       })
diff --git a/lib/getCookieOpts.js b/lib/getCookieOpts.js
deleted file mode 100644
index a951369..0000000
--- a/lib/getCookieOpts.js
+++ /dev/null
@@ -1,35 +0,0 @@
-'use strict'
-
-const isConnectionSecure = require('./isConnectionSecure')
-
-module.exports = function getCookieOpts (cookieOpts, request) {
-  const originalMaxAge = cookieOpts.originalMaxAge || cookieOpts.maxAge || null
-  let secure = cookieOpts.secure ?? null
-  let sameSite = cookieOpts.sameSite || null
-  let expires = null
-
-  if (originalMaxAge) {
-    expires = new Date(Date.now() + originalMaxAge)
-  } else if (cookieOpts.expires) {
-    expires = new Date(cookieOpts.expires)
-  }
-
-  if (secure === 'auto') {
-    if (isConnectionSecure(request)) {
-      secure = true
-    } else {
-      sameSite = 'Lax'
-      secure = false
-    }
-  }
-
-  return {
-    expires,
-    originalMaxAge,
-    sameSite,
-    secure,
-    path: cookieOpts.path || '/',
-    httpOnly: cookieOpts.httpOnly !== undefined ? cookieOpts.httpOnly : true,
-    domain: cookieOpts.domain || null
-  }
-}
diff --git a/lib/session.js b/lib/session.js
index da05050..55c7dd5 100644
--- a/lib/session.js
+++ b/lib/session.js
@@ -2,7 +2,7 @@
 
 const crypto = require('crypto')
 
-const getCookieOpts = require('./getCookieOpts')
+const Cookie = require('./cookie')
 const { configure: configureStringifier } = require('safe-stable-stringify')
 
 const stringify = configureStringifier({ bigint: false })
@@ -38,7 +38,7 @@ module.exports = class Session {
       prevSession[sessionIdKey] === sessionId &&
       prevSession[encryptedSessionIdKey]
     ) || cookieSigner.sign(this.sessionId)
-    this.cookie = getCookieOpts(prevSession?.cookie || cookieOpts, request)
+    this.cookie = new Cookie(prevSession?.cookie || cookieOpts, request)
 
     if (prevSession) {
       // Copy over values from the previous session
diff --git a/test/cookie.test.js b/test/cookie.test.js
index bc3ad02..a24c0bc 100644
--- a/test/cookie.test.js
+++ b/test/cookie.test.js
@@ -5,6 +5,7 @@ const Fastify = require('fastify')
 const fastifyCookie = require('@fastify/cookie')
 const fastifySession = require('../lib/fastifySession')
 const fastifyPlugin = require('fastify-plugin')
+const Cookie = require('../lib/cookie')
 const { DEFAULT_OPTIONS, DEFAULT_COOKIE, DEFAULT_SECRET, buildFastify, DEFAULT_SESSION_ID } = require('./util')
 
 test('should set session cookie', async (t) => {
@@ -502,3 +503,56 @@ test('when cookie secure is set to false then store secure as false', async t =>
   t.equal(typeof response.headers['set-cookie'], 'string')
   t.match(response.headers['set-cookie'], /^sessionId=[\w-]{32}.[\w-%]{43,135}; Path=\/; HttpOnly$/)
 })
+
+test('Cookie', t => {
+  t.plan(4)
+
+  const cookie = new Cookie({})
+
+  t.test('properties', t => {
+    t.plan(9)
+
+    t.equal('expires' in cookie, true)
+    t.equal('originalMaxAge' in cookie, true)
+    t.equal('sameSite' in cookie, true)
+    t.equal('secure' in cookie, true)
+    t.equal('path' in cookie, true)
+    t.equal('httpOnly' in cookie, true)
+    t.equal('domain' in cookie, true)
+    t.equal('_expires' in cookie, true)
+    t.equal('maxAge' in cookie, true)
+  })
+
+  t.test('toJSON', t => {
+    t.plan(9)
+
+    const json = cookie.toJSON()
+
+    t.equal('expires' in json, true)
+    t.equal('originalMaxAge' in json, true)
+    t.equal('sameSite' in json, true)
+    t.equal('secure' in json, true)
+    t.equal('path' in json, true)
+    t.equal('httpOnly' in json, true)
+    t.equal('domain' in json, true)
+
+    t.equal('_expires' in json, false)
+    t.equal('maxAge' in json, false)
+  })
+
+  t.test('maxAge calculated from expires', t => {
+    t.plan(2)
+
+    const cookie = new Cookie({ expires: new Date(Date.now() + 1000) })
+    t.equal(cookie.maxAge <= 1000, true)
+    t.equal(cookie.originalMaxAge, null)
+  })
+
+  t.test('maxAge set by maxAge', t => {
+    t.plan(2)
+
+    const cookie = new Cookie({ maxAge: 1000 })
+    t.equal(cookie.maxAge, 1000)
+    t.equal(cookie.originalMaxAge, 1000)
+  })
+})