diff --git a/README.md b/README.md
index 3462c91..c75b215 100644
--- a/README.md
+++ b/README.md
@@ -46,7 +46,7 @@ reproduced locally with one command.
 | Console and network | JavaScript errors, theme assets that 404, libraries loaded from third-party CDNs. |
 | Layout | Pages that scroll sideways at phone, tablet or desktop width, with the elements sticking out. |
 | Accessibility | [axe](https://github.com/dequelabs/axe-core) violations rated critical or serious, in light and dark mode. Keyboard basics: skip link, visible focus, menus that open and close with the keyboard. |
-| Performance | [Lighthouse](https://github.com/GoogleChrome/lighthouse) scores for the homepage and a post, against a budget per theme. |
+| Performance | [Lighthouse](https://github.com/GoogleChrome/lighthouse) scores for the homepage and a post, against a budget per theme. Ghost's own apps (Portal, search, comments) are blocked during the run, so the score is the theme's. |
 | Visual changes | On pull requests: every template at phone, tablet and desktop widths, in light and dark mode, before and after the change. Anything that looks different waits for a reviewer's approval. |
 
 Problems inside what Ghost renders itself (Portal, search, comments, the
diff --git a/test/theme.test.mjs b/test/theme.test.mjs
index d099ab1..313e175 100644
--- a/test/theme.test.mjs
+++ b/test/theme.test.mjs
@@ -1,4 +1,4 @@
-import { test } from 'node:test';
+import { mock, test } from 'node:test';
 import assert from 'node:assert/strict';
 import { execFileSync } from 'node:child_process';
 import { mkdirSync, mkdtempSync, rmSync, utimesSync, writeFileSync } from 'node:fs';
@@ -7,6 +7,11 @@ import { join } from 'node:path';
 import yauzl from 'yauzl';
 import { packageTheme } from '../src/theme.mjs';
 
+// packageTheme prints "── Zip: …". Plain text on stdout next to the test
+// runner's own messages makes `node --test` fail now and then with "Unable to
+// deserialize cloned data", so keep it quiet.
+mock.method(console, 'log', () => {});
+
 function config(dir, zip = {}) {
   return { dir, name: 'my-theme', pkg: {}, zip: { command: null, path: null, ...zip } };
 }
diff --git a/tests/lib/ghost.mjs b/tests/lib/ghost.mjs
index 34673cb..92745d5 100644
--- a/tests/lib/ghost.mjs
+++ b/tests/lib/ghost.mjs
@@ -32,6 +32,9 @@ export function isHtml(response) {
 /** Same-origin paths served by Ghost itself rather than the theme. */
 const GHOST_PATHS = ['/public/', '/ghost/', '/members/'];
 
+/** Ghost's apps (Portal, search, comments, …), as a Lighthouse `blockedUrlPatterns` entry. */
+export const GHOST_APPS = 'https://cdn.jsdelivr.net/ghost/*';
+
 /**
  * Third-party origins Ghost loads on its own: its apps from jsDelivr, fonts
  * from Bunny Fonts when a site picks a custom font, avatars from Gravatar.
diff --git a/tests/lighthouse.spec.mjs b/tests/lighthouse.spec.mjs
index 7920822..257bd5f 100644
--- a/tests/lighthouse.spec.mjs
+++ b/tests/lighthouse.spec.mjs
@@ -1,12 +1,18 @@
 // Lighthouse (mobile preset) for pages marked `lighthouse: true`, first profile
 // only. Runs on its own, in one worker, after the other checks so scores aren't
 // skewed by parallel load. Scores are attached and printed by the runner as a table.
+//
+// Ghost's own apps (Portal, search, comments) are blocked. The theme can't
+// change them, and on CI runners, with a slow CPU and a fast network,
+// Lighthouse's simulation counted Portal's half a megabyte towards the largest
+// paint: Pod lost 15 to 20 points that had nothing to do with the theme.
 
 import { createServer } from 'node:net';
 import { chromium } from '@playwright/test';
 import lighthouse from 'lighthouse';
 import { test, expect } from './fixtures.mjs';
 import { runtime, LIGHTHOUSE } from './lib/runtime.mjs';
+import { GHOST_APPS } from './lib/ghost.mjs';
 
 /** Lighthouse drives Chromium over a debugging port; ask the OS for a free one. */
 function freePort() {
@@ -34,6 +40,7 @@ for (const entry of runtime.manifest.pages.filter((p) => p.lighthouse)) {
         output: 'html',
         logLevel: 'error',
         onlyCategories: Object.keys(runtime.budgets),
+        blockedUrlPatterns: [GHOST_APPS],
       });
       const scores = Object.fromEntries(
         Object.entries(result.lhr.categories).map(([id, category]) => [id, category.score]),