diff --git a/README.md b/README.md
index c1376c0..5c8c99c 100644
--- a/README.md
+++ b/README.md
@@ -61,6 +61,8 @@ Note that the rest of the application may manipulate the array during its life c
 This can be used to rotate the signing secret at regular intervals. A secret should remain somewhere in the array as long as there are active sessions with cookies signed by it. Secrets management is left up to the rest of the application.
 ##### cookieName (optional)
 The name of the session cookie. Defaults to `sessionId`.
+##### cookiePrefix (optional)
+Prefix for the value of the cookie. This is useful for compatibility with `express-session`, which prefixes all cookies with `"s:"`. Defaults to `""`.
 ##### cookie
 The options object is used to generate the `Set-Cookie` header of the session cookie. May have the following properties:
 * `path` - The `Path` attribute. Defaults to `/` (the root path).
diff --git a/lib/fastifySession.js b/lib/fastifySession.js
index cf93989..21361d0 100644
--- a/lib/fastifySession.js
+++ b/lib/fastifySession.js
@@ -106,7 +106,12 @@ function decryptSession (sessionId, options, request, done) {
 function onRequest (options) {
   const unsignSignedCookie = options.unsignSignedCookie
   const cookieOpts = options.cookie
+  const cookieName = options.cookieName
   const idGenerator = options.idGenerator
+  const cookiePrefix = options.cookiePrefix
+  const hasCookiePrefix = typeof cookiePrefix === 'string' && cookiePrefix.length !== 0
+  const cookiePrefixLength = hasCookiePrefix && cookiePrefix.length
+
   return function handleSession (request, reply, done) {
     request.session = {}
 
@@ -115,7 +120,10 @@ function onRequest (options) {
       done()
       return
     }
-    const sessionId = request.cookies[options.cookieName]
+    let sessionId = request.cookies[cookieName]
+    if (sessionId && hasCookiePrefix && sessionId.startsWith(cookiePrefix)) {
+      sessionId = sessionId.slice(cookiePrefixLength)
+    }
     const secret = options.secret[0]
     if (!sessionId) {
       newSession(secret, request, cookieOpts, idGenerator, done)
@@ -135,6 +143,12 @@ function onRequest (options) {
 }
 
 function onSend (options) {
+  const cookieOpts = options.cookie
+  const cookieName = options.cookieName
+  const cookiePrefix = options.cookiePrefix
+  const saveUninitialized = options.saveUninitialized
+  const hasCookiePrefix = typeof cookiePrefix === 'string' && cookiePrefix.length !== 0
+
   return function saveSession (request, reply, payload, done) {
     const session = request.session
     if (!session || !session.sessionId) {
@@ -142,10 +156,15 @@ function onSend (options) {
       return
     }
 
-    if (!shouldSaveSession(request, options.cookie, options.saveUninitialized)) {
+    let encryptedSessionId = session.encryptedSessionId
+    if (encryptedSessionId && hasCookiePrefix) {
+      encryptedSessionId = `${cookiePrefix}${encryptedSessionId}`
+    }
+
+    if (!shouldSaveSession(request, cookieOpts, saveUninitialized)) {
       // if a session cookie is set, but has a different ID, clear it
-      if (request.cookies[options.cookieName] && request.cookies[options.cookieName] !== session.encryptedSessionId) {
-        reply.clearCookie(options.cookieName)
+      if (request.cookies[cookieName] && request.cookies[cookieName] !== encryptedSessionId) {
+        reply.clearCookie(cookieName)
       }
       done()
       return
@@ -156,8 +175,8 @@ function onSend (options) {
         return
       }
       reply.setCookie(
-        options.cookieName,
-        session.encryptedSessionId,
+        cookieName,
+        encryptedSessionId,
         session.cookie.options(isConnectionSecure(request))
       )
       done()
@@ -196,6 +215,7 @@ function ensureDefaults (options) {
   options.rolling = option(options, 'rolling', true)
   options.saveUninitialized = option(options, 'saveUninitialized', true)
   options.secret = Array.isArray(options.secret) ? options.secret : [options.secret]
+  options.cookiePrefix = option(options, 'cookiePrefix', '')
   return options
 }
 
diff --git a/test/base.test.js b/test/base.test.js
index aba1323..d0803b0 100644
--- a/test/base.test.js
+++ b/test/base.test.js
@@ -127,6 +127,40 @@ test('should set session cookie using the default cookie name', async (t) => {
   t.match(response.headers['set-cookie'], /sessionId=undefined; Path=\/; HttpOnly; Secure/)
 })
 
+test('should set express sessions using the specified cookiePrefix', async (t) => {
+  t.plan(2)
+  const options = {
+    secret: 'cNaoPYAwF60HZJzkcNaoPYAwF60HZJzk',
+    cookieName: 'connect.sid',
+    cookiePrefix: 's:'
+  }
+
+  const plugin = fastifyPlugin(async (fastify, opts) => {
+    fastify.addHook('onRequest', (request, reply, done) => {
+      request.sessionStore.set('Qk_XT2K7-clT-x1tVvoY6tIQ83iP72KN', {
+        expires: Date.now() + 1000
+      }, done)
+    })
+  })
+  function handler (request, reply) {
+    request.session.test = {}
+    reply.send(200)
+  }
+  const fastify = await buildFastify(handler, options, plugin)
+  t.teardown(() => fastify.close())
+
+  const response = await fastify.inject({
+    url: '/',
+    headers: {
+      cookie: 'connect.sid=s%3AQk_XT2K7-clT-x1tVvoY6tIQ83iP72KN.B7fUDYXU9fXF9pNuL3qm4NVmSduLJ6kzCOPh5JhHGoE; Path=/; HttpOnly; Secure',
+      'x-forwarded-proto': 'https'
+    }
+  })
+
+  t.equal(response.statusCode, 200)
+  t.match(response.headers['set-cookie'], /connect.sid=s%3A[\w-]{32}.[\w-%]{43,57}; Path=\/; HttpOnly; Secure/)
+})
+
 test('should create new session on expired session', async (t) => {
   t.plan(2)
   const plugin = fastifyPlugin(async (fastify, opts) => {
diff --git a/types/types.d.ts b/types/types.d.ts
index 3e7ee51..51b96f4 100644
--- a/types/types.d.ts
+++ b/types/types.d.ts
@@ -125,6 +125,12 @@ declare namespace FastifySessionPlugin {
 
     /** Function used to generate new session IDs. Defaults to uid(24). */
     idGenerator?(request?: Fastify.FastifyRequest): string;
+
+    /**
+     * Prefixes all cookie values. Run with "s:" to be be compatible with express-session.
+     * Defaults to ""
+     */
+     cookiePrefix?: string;
   }
 
   interface CookieOptions {