diff --git a/docs/docs/api/DiagnosticsChannel.md b/docs/docs/api/DiagnosticsChannel.md
index acf25e08218..cff8546f6f0 100644
--- a/docs/docs/api/DiagnosticsChannel.md
+++ b/docs/docs/api/DiagnosticsChannel.md
@@ -182,22 +182,24 @@ diagnosticsChannel.channel('undici:websocket:open').subscribe(({
   console.log(websocket) // the WebSocket instance
   
   // Handshake response details
-  console.log(handshakeResponse.status) // 101 for successful WebSocket upgrade
-  console.log(handshakeResponse.statusText) // 'Switching Protocols'
+  console.log(handshakeResponse.status) // 101 for HTTP/1.1, 200 for HTTP/2 extended CONNECT
+  console.log(handshakeResponse.statusText) // 'Switching Protocols' for HTTP/1.1, commonly 'OK' for HTTP/2 in Node.js
   console.log(handshakeResponse.headers) // Object containing response headers
 })
 ```
 
 ### Handshake Response Object
 
-The `handshakeResponse` object contains the HTTP response that upgraded the connection to WebSocket:
+The `handshakeResponse` object contains the HTTP response that established the WebSocket connection:
 
-- `status` (number): The HTTP status code (101 for successful WebSocket upgrade)
-- `statusText` (string): The HTTP status message ('Switching Protocols' for successful upgrade)
+- `status` (number): The HTTP status code (`101` for HTTP/1.1 upgrade, `200` for HTTP/2 extended CONNECT)
+- `statusText` (string): The HTTP status message (`'Switching Protocols'` for HTTP/1.1, commonly `'OK'` for HTTP/2 in Node.js)
 - `headers` (object): The HTTP response headers from the server, including:
+  - `sec-websocket-accept` and other WebSocket-related headers
   - `upgrade: 'websocket'`
   - `connection: 'upgrade'`
-  - `sec-websocket-accept` and other WebSocket-related headers
+
+  The `upgrade` and `connection` headers are only present for HTTP/1.1 handshakes.
 
 This information is particularly useful for debugging and monitoring WebSocket connections, as it provides access to the initial HTTP handshake response that established the WebSocket connection.
 
diff --git a/lib/core/diagnostics.js b/lib/core/diagnostics.js
index ccd6870ca6d..454ab379be3 100644
--- a/lib/core/diagnostics.js
+++ b/lib/core/diagnostics.js
@@ -177,10 +177,12 @@ function trackWebSocketEvents (debugLog = websocketDebuglog) {
 
   diagnosticsChannel.subscribe('undici:websocket:open',
     evt => {
-      const {
-        address: { address, port }
-      } = evt
-      debugLog('connection opened %s%s', address, port ? `:${port}` : '')
+      if (evt.address != null) {
+        const { address, port } = evt.address
+        debugLog('connection opened %s%s', address, port ? `:${port}` : '')
+      } else {
+        debugLog('connection opened')
+      }
     })
 
   diagnosticsChannel.subscribe('undici:websocket:close',
diff --git a/lib/web/websocket/websocket.js b/lib/web/websocket/websocket.js
index 64ead0d41c3..da94ab5b352 100644
--- a/lib/web/websocket/websocket.js
+++ b/lib/web/websocket/websocket.js
@@ -25,6 +25,18 @@ const { SendQueue } = require('./sender')
 const { WebsocketFrameSend } = require('./frame')
 const { channels } = require('../../core/diagnostics')
 
+function getSocketAddress (socket) {
+  if (typeof socket?.address === 'function') {
+    return socket.address()
+  }
+
+  if (typeof socket?.session?.socket?.address === 'function') {
+    return socket.session.socket.address()
+  }
+
+  return null
+}
+
 /**
  * @typedef {object} Handler
  * @property {(response: any, extensions?: string[]) => void} onConnectionEstablished
@@ -491,7 +503,7 @@ class WebSocket extends EventTarget {
       // Convert headers to a plain object for the event
       const headers = response.headersList.entries
       channels.open.publish({
-        address: response.socket.address(),
+        address: getSocketAddress(response.socket),
         protocol: this.#protocol,
         extensions: this.#extensions,
         websocket: this,
diff --git a/test/websocket/diagnostics-channel-handshake-response-h2.js b/test/websocket/diagnostics-channel-handshake-response-h2.js
new file mode 100644
index 00000000000..89abd69530d
--- /dev/null
+++ b/test/websocket/diagnostics-channel-handshake-response-h2.js
@@ -0,0 +1,84 @@
+'use strict'
+
+const { test } = require('node:test')
+const dc = require('node:diagnostics_channel')
+const { once } = require('node:events')
+const { createSecureServer } = require('node:http2')
+const { WebSocketServer, WebSocket: WSWebsocket } = require('ws')
+const { key, cert } = require('@metcoder95/https-pem')
+const { Agent, WebSocket } = require('../..')
+const { uid } = require('../../lib/web/websocket/constants')
+const { runtimeFeatures } = require('../../lib/util/runtime-features')
+
+const crypto = runtimeFeatures.has('crypto')
+  ? require('node:crypto')
+  : null
+
+test('diagnostics channel - undici:websocket:open includes handshake response over h2', { skip: crypto == null }, async (t) => {
+  t.plan(9)
+
+  const server = createSecureServer({ cert, key, settings: { enableConnectProtocol: true } })
+  const wsServer = new WebSocketServer({ noServer: true })
+
+  server.on('stream', (stream, headers) => {
+    stream.respond({
+      ':status': 200,
+      'sec-websocket-accept': crypto.hash('sha1', `${headers['sec-websocket-key']}${uid}`, 'base64')
+    })
+
+    const ws = new WSWebsocket(null, null, { autoPong: true })
+    ws.setSocket(stream, Buffer.alloc(0), {
+      maxPayload: 104857600,
+      skipUTF8Validation: false
+    })
+
+    wsServer.emit('connection', ws, stream)
+  })
+
+  wsServer.on('connection', (ws) => {
+    setTimeout(() => {
+      ws.close(1000, 'test')
+    }, 50)
+  })
+
+  server.listen(0)
+  await once(server, 'listening')
+
+  const dispatcher = new Agent({
+    allowH2: true,
+    connect: {
+      rejectUnauthorized: false
+    }
+  })
+
+  const openListener = (data) => {
+    t.assert.ok(data.address, 'address should be defined')
+    t.assert.strictEqual(typeof data.address.address, 'string', 'address.address should be a string')
+    t.assert.strictEqual(typeof data.address.port, 'number', 'address.port should be a number')
+    t.assert.ok(data.handshakeResponse, 'handshakeResponse should be defined')
+    t.assert.strictEqual(data.handshakeResponse.status, 200, 'status should be 200')
+    t.assert.strictEqual(data.handshakeResponse.statusText, 'OK', 'statusText should be OK for h2')
+    t.assert.ok(data.handshakeResponse.headers, 'headers should be defined')
+    t.assert.ok(typeof data.handshakeResponse.headers === 'object', 'headers should be an object')
+    t.assert.ok(typeof data.handshakeResponse.headers['sec-websocket-accept'] === 'string', 'sec-websocket-accept header should be a string')
+  }
+
+  dc.channel('undici:websocket:open').subscribe(openListener)
+
+  const ws = new WebSocket(`wss://localhost:${server.address().port}`, { dispatcher })
+
+  t.after(async () => {
+    dc.channel('undici:websocket:open').unsubscribe(openListener)
+    server.close()
+    await dispatcher.close()
+    await new Promise((resolve) => wsServer.close(resolve))
+  })
+
+  await Promise.race([
+    once(ws, 'open'),
+    once(ws, 'error').then(([event]) => {
+      throw event.error ?? new Error('unexpected websocket error')
+    })
+  ])
+  await once(ws, 'close')
+})