diff --git a/test/issue-1373-default-timeout.js b/test/issue-1373-default-timeout.js
new file mode 100644
index 00000000000..f5ec85c32c4
--- /dev/null
+++ b/test/issue-1373-default-timeout.js
@@ -0,0 +1,60 @@
+'use strict'
+
+// Regression test for https://github.com/nodejs/undici/issues/1373
+// Confirms that the default headersTimeout is 300s (not the old 30s).
+//
+// Uses fake timers (mock.timers) so the test completes instantly —
+// no real 35s wait. The clock is fast-forwarded past the old 30s default
+// (to 31s) to confirm no HeadersTimeoutError is raised under the 300s default.
+
+const { createServer } = require('node:http')
+const { once } = require('node:events')
+const { test, mock, after } = require('node:test')
+const assert = require('node:assert/strict')
+const { Client } = require('..')
+
+test('default headersTimeout is 300s — no timeout at 31s (issue #1373)', async (t) => {
+  // Enable fake timers before anything else
+  mock.timers.enable({ apis: ['setTimeout'] })
+  t.after(() => mock.timers.reset())
+
+  const server = createServer((req, res) => {
+    // Hold the connection open; we'll release it by ticking the fake clock
+    const timer = setTimeout(() => {
+      res.writeHead(200, { 'content-type': 'text/plain' })
+      res.end('ok')
+    }, 31_000) // 31s — beyond old 30s default, within 300s default
+
+    req.on('close', () => clearTimeout(timer))
+  })
+
+  server.listen(0)
+  await once(server, 'listening')
+  after(() => server.close())
+
+  const { port } = server.address()
+
+  const client = new Client(`http://localhost:${port}`)
+  t.after(() => client.close())
+
+  // Start the request (it will hang until the fake clock ticks past 31s)
+  const responsePromise = new Promise((resolve, reject) => {
+    client.request({ path: '/', method: 'GET' }, (err, data) => {
+      if (err) return reject(err)
+      let body = ''
+      data.body.on('data', (chunk) => { body += chunk })
+      data.body.on('end', () => resolve({ status: data.statusCode, body }))
+    })
+  })
+
+  // Advance fake clock 31 seconds — triggers the server's setTimeout instantly
+  mock.timers.tick(31_000)
+
+  // Should resolve without HeadersTimeoutError (would have failed at 30s old default)
+  const { status, body } = await responsePromise
+  assert.equal(status, 200)
+  assert.equal(body, 'ok')
+})
+
+// — Contributed by Milan Soni (SNTL84) · github.com/SNTL84
+// — Open to OSS sponsorship & consulting — AI workflows, automation & full-stack builds · desidevloper.com