diff --git a/packages/playwright-core/src/remote/playwrightServer.ts b/packages/playwright-core/src/remote/playwrightServer.ts
index bd60b8815d..f907018bf0 100644
--- a/packages/playwright-core/src/remote/playwrightServer.ts
+++ b/packages/playwright-core/src/remote/playwrightServer.ts
@@ -27,7 +27,7 @@ import { ManualPromise } from '../utils/manualPromise';
 import type { AndroidDevice } from '../server/android/android';
 import type { SocksProxy } from '../common/socksProxy';
 import { debugLogger } from '../common/debugLogger';
-import { createHttpServer } from '../utils';
+import { createHttpServer, userAgentVersionMatchesErrorMessage } from '../utils';
 import { perMessageDeflate } from '../server/transport';
 
 let lastConnectionId = 0;
@@ -45,6 +45,7 @@ type ServerOptions = {
 export class PlaywrightServer {
   private _preLaunchedPlaywright: Playwright | undefined;
   private _wsServer: WebSocketServer | undefined;
+  private _server: http.Server | undefined;
   private _options: ServerOptions;
 
   constructor(options: ServerOptions) {
@@ -69,6 +70,7 @@ export class PlaywrightServer {
       response.end('Running');
     });
     server.on('error', error => debugLogger.log('server', String(error)));
+    this._server = server;
 
     const wsEndpoint = await new Promise<string>((resolve, reject) => {
       server.listen(port, () => {
@@ -84,8 +86,7 @@ export class PlaywrightServer {
 
     debugLogger.log('server', 'Listening at ' + wsEndpoint);
     this._wsServer = new wsServer({
-      server,
-      path: this._options.path,
+      noServer: true,
       perMessageDeflate,
     });
     const browserSemaphore = new Semaphore(this._options.maxConnections);
@@ -96,6 +97,23 @@ export class PlaywrightServer {
         headers.push(process.env.PWTEST_SERVER_WS_HEADERS!);
       });
     }
+    server.on('upgrade', (request, socket, head) => {
+      const pathname = new URL('http://localhost' + request.url!).pathname;
+      if (pathname !== this._options.path) {
+        socket.write(`HTTP/${request.httpVersion} 400 Bad Request\r\n\r\n`);
+        socket.destroy();
+        return;
+      }
+
+      const uaError = userAgentVersionMatchesErrorMessage(request.headers['user-agent'] || '');
+      if (uaError) {
+        socket.write(`HTTP/${request.httpVersion} 428 Precondition Required\r\n\r\n${uaError}`);
+        socket.destroy();
+        return;
+      }
+
+      this._wsServer?.handleUpgrade(request, socket, head, ws => this._wsServer?.emit('connection', ws, request));
+    });
     this._wsServer.on('connection', (ws, request) => {
       debugLogger.log('server', 'Connected client ws.extension=' + ws.extensions);
       const url = new URL('http://localhost' + (request.url || ''));
@@ -171,8 +189,10 @@ export class PlaywrightServer {
     }));
     await waitForClose;
     debugLogger.log('server', 'closing http server');
-    await new Promise(f => server.options.server!.close(f));
+    if (this._server)
+      await new Promise(f => this._server!.close(f));
     this._wsServer = undefined;
+    this._server = undefined;
     debugLogger.log('server', 'closed server');
 
     debugLogger.log('server', 'closing browsers');
diff --git a/packages/playwright-core/src/utils/userAgent.ts b/packages/playwright-core/src/utils/userAgent.ts
index f2c2cb0037..17b1bc51c8 100644
--- a/packages/playwright-core/src/utils/userAgent.ts
+++ b/packages/playwright-core/src/utils/userAgent.ts
@@ -17,6 +17,7 @@
 import { execSync } from 'child_process';
 import os from 'os';
 import { getLinuxDistributionInfoSync } from '../utils/linuxUtils';
+import { wrapInASCIIBox } from './ascii';
 
 let cachedUserAgent: string | undefined;
 
@@ -76,8 +77,31 @@ export function getEmbedderName(): { embedderName: string, embedderVersion: stri
 }
 
 export function getPlaywrightVersion(majorMinorOnly = false): string {
-  const packageJson = require('./../../package.json');
-  if (process.env.PW_VERSION_OVERRIDE)
-    return process.env.PW_VERSION_OVERRIDE;
-  return majorMinorOnly ? packageJson.version.split('.').slice(0, 2).join('.') : packageJson.version;
+  const version = process.env.PW_VERSION_OVERRIDE || require('./../../package.json').version;
+  return majorMinorOnly ? version.split('.').slice(0, 2).join('.') : version;
+}
+
+export function userAgentVersionMatchesErrorMessage(userAgent: string) {
+  const match = userAgent.match(/^Playwright\/(\d+\.\d+\.\d+)/);
+  if (!match) {
+    // Cannot parse user agent - be lax.
+    return;
+  }
+  const received = match[1].split('.').slice(0, 2).join('.');
+  const expected = getPlaywrightVersion(true);
+  if (received !== expected) {
+    return wrapInASCIIBox([
+      `Playwright version mismatch:`,
+      `  - server version: v${expected}`,
+      `  - client version: v${received}`,
+      ``,
+      `If you are using VSCode extension, restart VSCode.`,
+      ``,
+      `If you are connecting to a remote service,`,
+      `keep your local Playwright version in sync`,
+      `with the remote service version.`,
+      ``,
+      `<3 Playwright Team`
+    ].join('\n'), 1);
+  }
 }
diff --git a/tests/config/remoteServer.ts b/tests/config/remoteServer.ts
index 2b81abba7c..34f6dcb4ca 100644
--- a/tests/config/remoteServer.ts
+++ b/tests/config/remoteServer.ts
@@ -27,7 +27,7 @@ export class RunServer implements PlaywrightServer {
   private _process: TestChildProcess;
   _wsEndpoint: string;
 
-  async start(childProcess: CommonFixtures['childProcess'], mode?: 'extension' | 'default') {
+  async start(childProcess: CommonFixtures['childProcess'], mode?: 'extension' | 'default', env?: NodeJS.ProcessEnv) {
     const command = ['node', path.join(__dirname, '..', '..', 'packages', 'playwright-core', 'lib', 'cli', 'cli.js'), 'run-server'];
     if (mode === 'extension')
       command.push('--mode=extension');
@@ -36,6 +36,7 @@ export class RunServer implements PlaywrightServer {
       env: {
         ...process.env,
         PWTEST_UNDER_TEST: '1',
+        ...env,
       },
     });
 
diff --git a/tests/library/browsertype-connect.spec.ts b/tests/library/browsertype-connect.spec.ts
index 89d58035de..b5d480c5d8 100644
--- a/tests/library/browsertype-connect.spec.ts
+++ b/tests/library/browsertype-connect.spec.ts
@@ -20,7 +20,7 @@ import os from 'os';
 import type http from 'http';
 import type net from 'net';
 import * as path from 'path';
-import { getUserAgent } from '../../packages/playwright-core/lib/utils/userAgent';
+import { getUserAgent, getPlaywrightVersion } from '../../packages/playwright-core/lib/utils/userAgent';
 import WebSocket from 'ws';
 import { expect, playwrightTest } from '../config/browserTest';
 import { parseTrace, suppressCertificateWarning } from '../config/utils';
@@ -28,6 +28,7 @@ import formidable from 'formidable';
 import type { Browser, ConnectOptions } from 'playwright-core';
 import { createHttpServer } from '../../packages/playwright-core/lib/utils/network';
 import { kTargetClosedErrorMessage } from '../config/errors';
+import { RunServer } from '../config/remoteServer';
 
 type ExtraFixtures = {
   connect: (wsEndpoint: string, options?: ConnectOptions, redirectPortForTest?: number) => Promise<Browser>,
@@ -914,3 +915,13 @@ test.describe('launchServer only', () => {
     }
   });
 });
+
+test('should refuse connecting when versions do not match', async ({ connect, childProcess }) => {
+  const server = new RunServer();
+  await server.start(childProcess, 'default', { PW_VERSION_OVERRIDE: '1.2.3' });
+  const error = await connect(server.wsEndpoint()).catch(e => e);
+  await server.close();
+  expect(error.message).toContain('Playwright version mismatch');
+  expect(error.message).toContain('server version: v1.2');
+  expect(error.message).toContain('client version: v' + getPlaywrightVersion(true));
+});