diff --git a/index.js b/index.js
index ad52b9e..0e4667a 100644
--- a/index.js
+++ b/index.js
@@ -97,7 +97,7 @@ class WebSocketProxy {
       headers: {},
       ...wsClientOptions
     }
-    this.upstream = convertUrlToWebSocket(upstream)
+    this.upstream = upstream ? convertUrlToWebSocket(upstream) : ''
     this.wsUpstream = wsUpstream ? convertUrlToWebSocket(wsUpstream) : ''
     this.getUpstream = getUpstream
 
@@ -229,7 +229,7 @@ function generateRewritePrefix (prefix, opts) {
 }
 
 async function fastifyHttpProxy (fastify, opts) {
-  if (!opts.upstream && !(opts.upstream === '' && opts.replyOptions && typeof opts.replyOptions.getUpstream === 'function')) {
+  if (!opts.upstream && !opts.websocket && !((opts.upstream === '' || opts.wsUpstream === '') && opts.replyOptions && typeof opts.replyOptions.getUpstream === 'function')) {
     throw new Error('upstream must be specified')
   }
 
diff --git a/test/websocket.js b/test/websocket.js
index a711895..50bb067 100644
--- a/test/websocket.js
+++ b/test/websocket.js
@@ -194,6 +194,74 @@ test('getUpstream', async (t) => {
   ])
 })
 
+test('getUpstream with unset wsUpstream', async (t) => {
+  t.plan(9)
+
+  const origin = createServer()
+  const wss = new WebSocket.Server({ server: origin })
+  t.teardown(wss.close.bind(wss))
+  t.teardown(origin.close.bind(origin))
+
+  const serverMessages = []
+  wss.on('connection', (ws, request) => {
+    t.equal(ws.protocol, subprotocolValue)
+    t.equal(request.headers.cookie, cookieValue)
+    ws.on('message', (message, binary) => {
+      serverMessages.push([message.toString(), binary])
+      // echo
+      ws.send(message, { binary })
+    })
+  })
+
+  await promisify(origin.listen.bind(origin))({ port: 0, host: '127.0.0.1' })
+
+  const server = Fastify()
+
+  let _req
+  server.server.on('upgrade', (req) => {
+    _req = req
+  })
+
+  server.register(proxy, {
+    wsUpstream: '',
+    replyOptions: {
+      getUpstream: function (original) {
+        t.not(original, _req)
+        t.equal(original.raw, _req)
+        return `http://127.0.0.1:${origin.address().port}`
+      }
+    },
+    websocket: true
+  })
+
+  await server.listen({ port: 0, host: '127.0.0.1' })
+  t.teardown(server.close.bind(server))
+
+  const options = { headers: { cookie: cookieValue } }
+  const ws = new WebSocket(`ws://127.0.0.1:${server.server.address().port}`, [subprotocolValue], options)
+  await once(ws, 'open')
+
+  ws.send('hello', { binary: false })
+  const [reply0, binary0] = await once(ws, 'message')
+  t.equal(reply0.toString(), 'hello')
+  t.equal(binary0, false)
+
+  ws.send(Buffer.from('fastify'), { binary: true })
+  const [reply1, binary1] = await once(ws, 'message')
+  t.equal(reply1.toString(), 'fastify')
+  t.equal(binary1, true)
+
+  t.strictSame(serverMessages, [
+    ['hello', false],
+    ['fastify', true]
+  ])
+
+  await Promise.all([
+    once(ws, 'close'),
+    server.close()
+  ])
+})
+
 test('websocket proxy trigger hooks', async (t) => {
   t.plan(8)