diff --git a/src/helpers/get-page-urls.ts b/src/helpers/get-page-urls.ts
index 30430b3..96bf66a 100644
--- a/src/helpers/get-page-urls.ts
+++ b/src/helpers/get-page-urls.ts
@@ -328,14 +328,21 @@ async function discoverSitemapUrls(ctx: CheckContext, originOverride?: string):
 
   // Build fallback candidates: origin-level sitemap first, then subpath sitemaps
   // when the base URL has a non-root path (e.g. swagger.io/docs/).
+  // Both `sitemap-index.xml` (hyphen) and `sitemap_index.xml` (underscore) are
+  // observed in the wild; e.g. Document360's CMS emits the underscore form.
   const fallbackOrigin = originOverride ?? ctx.origin;
-  const candidates = [`${fallbackOrigin}/sitemap.xml`];
+  const candidates = [
+    `${fallbackOrigin}/sitemap.xml`,
+    `${fallbackOrigin}/sitemap-index.xml`,
+    `${fallbackOrigin}/sitemap_index.xml`,
+  ];
 
   const baseUrlPath = new URL(ctx.baseUrl).pathname.replace(/\/$/, '');
   if (baseUrlPath && baseUrlPath !== '') {
     const subpathBase = `${fallbackOrigin}${baseUrlPath}`;
     candidates.push(`${subpathBase}/sitemap.xml`);
     candidates.push(`${subpathBase}/sitemap-index.xml`);
+    candidates.push(`${subpathBase}/sitemap_index.xml`);
   }
 
   return candidates;
diff --git a/test/helpers/mock-sitemap-not-found.ts b/test/helpers/mock-sitemap-not-found.ts
index 2b30fda..63e24bc 100644
--- a/test/helpers/mock-sitemap-not-found.ts
+++ b/test/helpers/mock-sitemap-not-found.ts
@@ -14,6 +14,8 @@ export function mockSitemapNotFound(server: SetupServerApi, baseUrl: string): vo
   const handlers = [
     http.get(`${parsed.origin}/robots.txt`, () => new HttpResponse('', { status: 404 })),
     http.get(`${parsed.origin}/sitemap.xml`, () => new HttpResponse('', { status: 404 })),
+    http.get(`${parsed.origin}/sitemap-index.xml`, () => new HttpResponse('', { status: 404 })),
+    http.get(`${parsed.origin}/sitemap_index.xml`, () => new HttpResponse('', { status: 404 })),
   ];
   const subpath = parsed.pathname.replace(/\/$/, '');
   if (subpath && subpath !== '') {
@@ -26,6 +28,10 @@ export function mockSitemapNotFound(server: SetupServerApi, baseUrl: string): vo
         `${parsed.origin}${subpath}/sitemap-index.xml`,
         () => new HttpResponse('', { status: 404 }),
       ),
+      http.get(
+        `${parsed.origin}${subpath}/sitemap_index.xml`,
+        () => new HttpResponse('', { status: 404 }),
+      ),
     );
   }
   server.use(...handlers);
diff --git a/test/integration/check-pipeline.test.ts b/test/integration/check-pipeline.test.ts
index 7beb6db..d6778a9 100644
--- a/test/integration/check-pipeline.test.ts
+++ b/test/integration/check-pipeline.test.ts
@@ -56,6 +56,8 @@ function setupSite(
   handlers.push(
     http.get(`http://${host}/robots.txt`, () => new HttpResponse('', { status: 404 })),
     http.get(`http://${host}/sitemap.xml`, () => new HttpResponse('', { status: 404 })),
+    http.get(`http://${host}/sitemap-index.xml`, () => new HttpResponse('', { status: 404 })),
+    http.get(`http://${host}/sitemap_index.xml`, () => new HttpResponse('', { status: 404 })),
   );
 
   const defaultCacheHeaders = opts.cacheControl ? { 'Cache-Control': opts.cacheControl } : {};
diff --git a/test/integration/cross-check-contracts.test.ts b/test/integration/cross-check-contracts.test.ts
index 7ab9170..ba383a1 100644
--- a/test/integration/cross-check-contracts.test.ts
+++ b/test/integration/cross-check-contracts.test.ts
@@ -150,6 +150,7 @@ describe('previousResults safety: checks handle missing dependencies gracefully'
       const ctx = createContext(`http://${host}`, { requestDelay: 0 });
       // No llms-txt-exists in previousResults, no llms.txt
 
+      mockSitemapNotFound(server, `http://${host}`);
       server.use(
         http.get(`http://${host}/llms.txt`, () => new HttpResponse(null, { status: 404 })),
         http.get(`http://${host}/docs/llms.txt`, () => new HttpResponse(null, { status: 404 })),
@@ -368,6 +369,7 @@ describe('cross-check field contracts: empty/missing upstream details', () => {
       details: { discoveredFiles: [] },
     });
 
+    mockSitemapNotFound(server, `http://${host}`);
     server.use(
       http.get(`http://${host}/llms.txt`, () => new HttpResponse(null, { status: 404 })),
       http.get(`http://${host}/docs/llms.txt`, () => new HttpResponse(null, { status: 404 })),
diff --git a/test/integration/dependency-chains.test.ts b/test/integration/dependency-chains.test.ts
index d1f90bd..f2ac05b 100644
--- a/test/integration/dependency-chains.test.ts
+++ b/test/integration/dependency-chains.test.ts
@@ -48,6 +48,8 @@ function setupSite(
     http.get(`http://${host}/docs/llms.txt`, () => new HttpResponse(null, { status: 404 })),
     http.get(`http://${host}/robots.txt`, () => new HttpResponse('', { status: 404 })),
     http.get(`http://${host}/sitemap.xml`, () => new HttpResponse('', { status: 404 })),
+    http.get(`http://${host}/sitemap-index.xml`, () => new HttpResponse('', { status: 404 })),
+    http.get(`http://${host}/sitemap_index.xml`, () => new HttpResponse('', { status: 404 })),
   );
 
   for (const page of opts.pages) {
diff --git a/test/integration/scoring-pipeline.test.ts b/test/integration/scoring-pipeline.test.ts
index 1c7aea6..875ade1 100644
--- a/test/integration/scoring-pipeline.test.ts
+++ b/test/integration/scoring-pipeline.test.ts
@@ -90,6 +90,10 @@ function setupSite(
       http.get(`http://${host}/sitemap.xml`, () => new HttpResponse('', { status: 404 })),
     );
   }
+  handlers.push(
+    http.get(`http://${host}/sitemap-index.xml`, () => new HttpResponse('', { status: 404 })),
+    http.get(`http://${host}/sitemap_index.xml`, () => new HttpResponse('', { status: 404 })),
+  );
 
   // Root URL for homepage-based discovery
   const pageLinks = opts.pages
@@ -415,6 +419,12 @@ describe('scoring pipeline: resolutions populated for real check failures', () =
   it('each failing check produces a resolution string', async () => {
     const { pages } = makePages(host, 6);
     setupSite(host, { pages, cacheControl: 'max-age=300' });
+    // No llms.txt or sitemap → discovery falls back to baseUrl, and
+    // markdown-url-support probes baseUrl's .md candidates.
+    server.use(
+      http.get(`http://${host}/.md`, () => new HttpResponse(null, { status: 404 })),
+      http.get(`http://${host}/index.md`, () => new HttpResponse(null, { status: 404 })),
+    );
 
     const report = await runChecks(`http://${host}`, {
       requestDelay: 0,
diff --git a/test/unit/checks/content-start-position.test.ts b/test/unit/checks/content-start-position.test.ts
index ba9e9da..964c067 100644
--- a/test/unit/checks/content-start-position.test.ts
+++ b/test/unit/checks/content-start-position.test.ts
@@ -480,6 +480,7 @@ describe('content-start-position', () => {
   // ── Fallback to baseUrl ──
 
   it('falls back to baseUrl when no llms.txt', async () => {
+    mockSitemapNotFound(server, 'http://csp-fb.local');
     server.use(
       http.get(
         'http://csp-fb.local/llms.txt',
diff --git a/test/unit/checks/llms-txt-coverage.test.ts b/test/unit/checks/llms-txt-coverage.test.ts
index c58e891..1a6b6df 100644
--- a/test/unit/checks/llms-txt-coverage.test.ts
+++ b/test/unit/checks/llms-txt-coverage.test.ts
@@ -4,6 +4,7 @@ import { setupServer } from 'msw/node';
 import { getCheck } from '../../../src/checks/registry.js';
 import { createContext } from '../../../src/runner.js';
 import type { DiscoveredFile } from '../../../src/types.js';
+import { mockSitemapNotFound } from '../../helpers/mock-sitemap-not-found.js';
 import {
   hasLocaleCodeAt,
   filterToUnprefixedLocale,
@@ -288,15 +289,7 @@ describe('llms-txt-coverage', () => {
     const host = 'cov-no-sitemap.local';
     const ctx = makeCtx(host, [`http://${host}/docs/page`], '/docs');
 
-    server.use(
-      http.get(`http://${host}/robots.txt`, () => new HttpResponse('', { status: 404 })),
-      http.get(`http://${host}/sitemap.xml`, () => new HttpResponse('', { status: 404 })),
-      http.get(`http://${host}/docs/sitemap.xml`, () => new HttpResponse('', { status: 404 })),
-      http.get(
-        `http://${host}/docs/sitemap-index.xml`,
-        () => new HttpResponse('', { status: 404 }),
-      ),
-    );
+    mockSitemapNotFound(server, `http://${host}/docs`);
 
     const result = await check.run(ctx);
     expect(result.status).toBe('skip');
@@ -527,10 +520,8 @@ describe('llms-txt-coverage', () => {
 
     const ctx = makeCtx(host, docPages, '/docs');
 
+    mockSitemapNotFound(server, `http://${host}/docs`);
     server.use(
-      // No main sitemap
-      http.get(`http://${host}/robots.txt`, () => new HttpResponse('', { status: 404 })),
-      http.get(`http://${host}/sitemap.xml`, () => new HttpResponse('', { status: 404 })),
       // Docs sitemap is an index
       http.get(
         `http://${host}/docs/sitemap.xml`,
@@ -548,10 +539,6 @@ describe('llms-txt-coverage', () => {
             headers: { 'content-type': 'application/xml' },
           }),
       ),
-      http.get(
-        `http://${host}/docs/sitemap-index.xml`,
-        () => new HttpResponse('', { status: 404 }),
-      ),
     );
 
     const result = await check.run(ctx);
diff --git a/test/unit/checks/markdown-url-support.test.ts b/test/unit/checks/markdown-url-support.test.ts
index d4c2f4f..b8dc754 100644
--- a/test/unit/checks/markdown-url-support.test.ts
+++ b/test/unit/checks/markdown-url-support.test.ts
@@ -603,6 +603,7 @@ describe('markdown-url-support', () => {
   // false-positive the check for a /auth/index.html page.
   it('does not test /foo.md when /foo/index.html came from sitemap (issue #77 isolation)', async () => {
     const requestLog: string[] = [];
+    mockSitemapNotFound(server, 'http://parentclean.local');
     server.use(
       http.get('http://parentclean.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
diff --git a/test/unit/checks/page-size-html.test.ts b/test/unit/checks/page-size-html.test.ts
index 58dea4d..f6116e0 100644
--- a/test/unit/checks/page-size-html.test.ts
+++ b/test/unit/checks/page-size-html.test.ts
@@ -308,6 +308,7 @@ describe('page-size-html', () => {
   });
 
   it('falls back to baseUrl when no llms.txt', async () => {
+    mockSitemapNotFound(server, 'http://ps-html-fb.local');
     server.use(
       http.get(
         'http://ps-html-fb.local/llms.txt',
diff --git a/test/unit/checks/page-size-markdown.test.ts b/test/unit/checks/page-size-markdown.test.ts
index 211aa37..77a9605 100644
--- a/test/unit/checks/page-size-markdown.test.ts
+++ b/test/unit/checks/page-size-markdown.test.ts
@@ -147,6 +147,7 @@ describe('page-size-markdown', () => {
 
   it('works in standalone mode when dependencies never ran', async () => {
     mockNoLlmsTxt('ps-md-standalone.local');
+    mockSitemapNotFound(server, 'http://ps-md-standalone.local');
     server.use(
       http.get(
         'http://ps-md-standalone.local/robots.txt',
@@ -187,6 +188,7 @@ describe('page-size-markdown', () => {
 
   it('skips in standalone mode when no markdown found', async () => {
     mockNoLlmsTxt('ps-md-nomd.local');
+    mockSitemapNotFound(server, 'http://ps-md-nomd.local');
     server.use(
       http.get('http://ps-md-nomd.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get('http://ps-md-nomd.local/sitemap.xml', () => new HttpResponse('', { status: 404 })),
diff --git a/test/unit/helpers/get-page-urls.test.ts b/test/unit/helpers/get-page-urls.test.ts
index 1ad7933..6b1d252 100644
--- a/test/unit/helpers/get-page-urls.test.ts
+++ b/test/unit/helpers/get-page-urls.test.ts
@@ -719,6 +719,7 @@ describe('getPageUrls', () => {
   });
 
   it('fetches and parses sitemap.xml when no llms.txt links', async () => {
+    mockSitemapNotFound(server, 'http://sitemap-test.local');
     server.use(
       http.get(
         'http://sitemap-test.local/robots.txt',
@@ -748,6 +749,7 @@ describe('getPageUrls', () => {
   });
 
   it('handles sitemap index files (follows sub-sitemaps)', async () => {
+    mockSitemapNotFound(server, 'http://index-test.local');
     server.use(
       http.get('http://index-test.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -784,6 +786,7 @@ describe('getPageUrls', () => {
   });
 
   it('filters sitemap URLs to same-origin only', async () => {
+    mockSitemapNotFound(server, 'http://origin-test.local');
     server.use(
       http.get('http://origin-test.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -810,6 +813,7 @@ describe('getPageUrls', () => {
   });
 
   it('falls back to baseUrl when both llms.txt and sitemap are empty', async () => {
+    mockSitemapNotFound(server, 'http://empty-test.local');
     server.use(
       http.get('http://empty-test.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -825,6 +829,7 @@ describe('getPageUrls', () => {
   });
 
   it('handles malformed sitemap XML gracefully', async () => {
+    mockSitemapNotFound(server, 'http://bad-xml.local');
     server.use(
       http.get('http://bad-xml.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -848,6 +853,7 @@ describe('getPageUrls', () => {
       (_, i) => `  <url><loc>http://big-sitemap.local/page/${i}</loc></url>`,
     ).join('\n');
 
+    mockSitemapNotFound(server, 'http://big-sitemap.local');
     server.use(
       http.get('http://big-sitemap.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -878,6 +884,7 @@ describe('getPageUrls', () => {
       (_, i) => `  <url><loc>http://cap-prefix.local/en/6.0/page/${i}</loc></url>`,
     ).join('\n');
 
+    mockSitemapNotFound(server, 'http://cap-prefix.local/en/6.0');
     server.use(
       http.get('http://cap-prefix.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -943,6 +950,7 @@ describe('getPageUrls', () => {
       .map((u) => `  <url><loc>${u}</loc></url>`)
       .join('\n');
 
+    mockSitemapNotFound(server, 'http://ver-dedup.local');
     server.use(
       http.get('http://ver-dedup.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -966,6 +974,7 @@ describe('getPageUrls', () => {
 
   it('filters sitemap index to default locale, skipping non-English sub-sitemaps (#30)', async () => {
     // Django-like sitemap index: 12 locale sitemaps, only en should be fetched
+    mockSitemapNotFound(server, 'http://locale-idx.local');
     server.use(
       http.get('http://locale-idx.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -1006,6 +1015,7 @@ describe('getPageUrls', () => {
   });
 
   it('handles sitemap fetch network errors gracefully', async () => {
+    mockSitemapNotFound(server, 'http://net-err.local');
     server.use(
       http.get('http://net-err.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get('http://net-err.local/sitemap.xml', () => HttpResponse.error()),
@@ -1085,6 +1095,7 @@ describe('getPageUrls', () => {
   });
 
   it('falls back to /sitemap.xml when robots.txt has no Sitemap directive', async () => {
+    mockSitemapNotFound(server, 'http://no-directive.local');
     server.use(
       http.get(
         'http://no-directive.local/robots.txt',
@@ -1107,6 +1118,95 @@ describe('getPageUrls', () => {
     expect(result.urls).toEqual(['http://no-directive.local/page']);
   });
 
+  it('falls back to /sitemap-index.xml at root when robots.txt lacks Sitemap directive and /sitemap.xml is absent', async () => {
+    server.use(
+      http.get(
+        'http://root-index.local/robots.txt',
+        () => new HttpResponse('User-agent: *\nAllow: /\n', { status: 200 }),
+      ),
+      http.get('http://root-index.local/sitemap.xml', () => new HttpResponse('', { status: 404 })),
+      http.get(
+        'http://root-index.local/sitemap_index.xml',
+        () => new HttpResponse('', { status: 404 }),
+      ),
+      http.get(
+        'http://root-index.local/sitemap-index.xml',
+        () =>
+          new HttpResponse(
+            `<?xml version="1.0"?>
+<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <sitemap><loc>http://root-index.local/sitemap-0.xml</loc></sitemap>
+</sitemapindex>`,
+            { status: 200, headers: { 'Content-Type': 'application/xml' } },
+          ),
+      ),
+      http.get(
+        'http://root-index.local/sitemap-0.xml',
+        () =>
+          new HttpResponse(
+            `<?xml version="1.0"?><urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <url><loc>http://root-index.local/page-a</loc></url>
+  <url><loc>http://root-index.local/page-b</loc></url>
+</urlset>`,
+            { status: 200, headers: { 'Content-Type': 'application/xml' } },
+          ),
+      ),
+    );
+
+    const ctx = makeCtx('http://root-index.local');
+    const result = await getPageUrls(ctx);
+    expect(result.urls).toEqual([
+      'http://root-index.local/page-a',
+      'http://root-index.local/page-b',
+    ]);
+  });
+
+  it('falls back to /sitemap_index.xml (underscore variant) at root when other candidates 404', async () => {
+    server.use(
+      http.get(
+        'http://underscore-index.local/robots.txt',
+        () => new HttpResponse('User-agent: *\nAllow: /\n', { status: 200 }),
+      ),
+      http.get(
+        'http://underscore-index.local/sitemap.xml',
+        () => new HttpResponse('', { status: 404 }),
+      ),
+      http.get(
+        'http://underscore-index.local/sitemap-index.xml',
+        () => new HttpResponse('', { status: 404 }),
+      ),
+      http.get(
+        'http://underscore-index.local/sitemap_index.xml',
+        () =>
+          new HttpResponse(
+            `<?xml version="1.0"?>
+<sitemapindex xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <sitemap><loc>http://underscore-index.local/sitemap-en.xml</loc></sitemap>
+</sitemapindex>`,
+            { status: 200, headers: { 'Content-Type': 'application/xml' } },
+          ),
+      ),
+      http.get(
+        'http://underscore-index.local/sitemap-en.xml',
+        () =>
+          new HttpResponse(
+            `<?xml version="1.0"?><urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
+  <url><loc>http://underscore-index.local/article-1</loc></url>
+  <url><loc>http://underscore-index.local/article-2</loc></url>
+</urlset>`,
+            { status: 200, headers: { 'Content-Type': 'application/xml' } },
+          ),
+      ),
+    );
+
+    const ctx = makeCtx('http://underscore-index.local');
+    const result = await getPageUrls(ctx);
+    expect(result.urls).toEqual([
+      'http://underscore-index.local/article-1',
+      'http://underscore-index.local/article-2',
+    ]);
+  });
+
   it('warns and skips gzipped sitemap from robots.txt', async () => {
     server.use(
       http.get(
@@ -1124,6 +1224,7 @@ describe('getPageUrls', () => {
   });
 
   it('warns and skips gzipped sub-sitemap from sitemap index', async () => {
+    mockSitemapNotFound(server, 'http://gz-index.local');
     server.use(
       http.get('http://gz-index.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -1446,6 +1547,7 @@ describe('getPageUrls', () => {
 
   it('fetches llms.txt directly when llms-txt-exists has not run', async () => {
     const llmsTxt = `# Docs\n> Summary\n## Links\n- [Intro](http://direct-llms.local/docs/intro): Intro\n- [Guide](http://direct-llms.local/docs/guide): Guide\n`;
+    mockSitemapNotFound(server, 'http://direct-llms.local');
     server.use(
       http.get(
         'http://direct-llms.local/llms.txt',
@@ -1470,6 +1572,7 @@ describe('getPageUrls', () => {
   });
 
   it('skips llms.txt with non-text content-type in standalone mode', async () => {
+    mockSitemapNotFound(server, 'http://nontext-llms.local');
     server.use(
       http.get(
         'http://nontext-llms.local/llms.txt',
@@ -1497,6 +1600,7 @@ describe('getPageUrls', () => {
   });
 
   it('skips llms.txt that returns HTML in standalone mode', async () => {
+    mockSitemapNotFound(server, 'http://html-llms.local');
     server.use(
       http.get(
         'http://html-llms.local/llms.txt',
@@ -1520,6 +1624,7 @@ describe('getPageUrls', () => {
   });
 
   it('skips empty llms.txt in standalone mode', async () => {
+    mockSitemapNotFound(server, 'http://empty-llms.local');
     server.use(
       http.get(
         'http://empty-llms.local/llms.txt',
@@ -1540,6 +1645,7 @@ describe('getPageUrls', () => {
   });
 
   it('handles llms.txt fetch errors gracefully in standalone mode', async () => {
+    mockSitemapNotFound(server, 'http://err-llms.local');
     server.use(
       http.get('http://err-llms.local/llms.txt', () => HttpResponse.error()),
       http.get('http://err-llms.local/docs/llms.txt', () => HttpResponse.error()),
@@ -1612,6 +1718,7 @@ describe('getPageUrls', () => {
   });
 
   it('scopes sitemap URLs to the baseUrl path prefix', async () => {
+    mockSitemapNotFound(server, 'http://sitemap-scope.local/docs');
     server.use(
       http.get(
         'http://sitemap-scope.local/robots.txt',
@@ -1651,6 +1758,7 @@ describe('getPageUrls', () => {
 
   it('discovers sitemap at docs subpath when origin-level sitemap is empty (#32)', async () => {
     // Simulate Swagger UI: robots.txt 404, /sitemap.xml 404, but /docs/sitemap-index.xml exists
+    mockSitemapNotFound(server, 'http://subpath-sm.local/docs');
     server.use(
       http.get('http://subpath-sm.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -1786,6 +1894,7 @@ describe('getPageUrls', () => {
   });
 
   it('explicit preferredLocale applies to sitemap index filtering', async () => {
+    mockSitemapNotFound(server, 'http://opt-sitemap-locale.local');
     server.use(
       http.get(
         'http://opt-sitemap-locale.local/robots.txt',
@@ -1829,6 +1938,7 @@ describe('getPageUrls', () => {
   });
 
   it('skipRefinement returns unfiltered sitemap URLs', async () => {
+    mockSitemapNotFound(server, 'http://skip-refine.local');
     server.use(
       http.get('http://skip-refine.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -1886,6 +1996,7 @@ describe('getPageUrls', () => {
   });
 
   it('respects maxUrls cap when following sitemap index sub-sitemaps', async () => {
+    mockSitemapNotFound(server, 'http://cap-index.local');
     server.use(
       http.get('http://cap-index.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
@@ -2214,6 +2325,7 @@ describe('originalMdUrls (issue #77)', () => {
       message: 'No llms.txt',
       details: { discoveredFiles: [] },
     });
+    mockSitemapNotFound(server, 'http://test77d.local');
     server.use(
       http.get('http://test77d.local/robots.txt', () => new HttpResponse('', { status: 404 })),
       http.get(
diff --git a/test/unit/runner.test.ts b/test/unit/runner.test.ts
index 80b7fab..043480a 100644
--- a/test/unit/runner.test.ts
+++ b/test/unit/runner.test.ts
@@ -4,6 +4,7 @@ import { setupServer } from 'msw/node';
 import { createContext, normalizeUrl, runChecks } from '../../src/runner.js';
 import { registerCheck } from '../../src/checks/registry.js';
 import '../../src/checks/index.js';
+import { mockSitemapNotFound } from '../helpers/mock-sitemap-not-found.js';
 
 const server = setupServer();
 
@@ -206,6 +207,7 @@ describe('runner', () => {
     // page-size-markdown depends on [['markdown-url-support', 'content-negotiation']]
     // When neither dependency runs (filtered out), page-size-markdown should still run
     // rather than being skipped.
+    mockSitemapNotFound(server, 'http://standalone.local');
     server.use(
       http.get('http://standalone.local/llms.txt', () => new HttpResponse(null, { status: 404 })),
       http.get(
@@ -429,6 +431,7 @@ describe('runner', () => {
   });
 
   it('includes timestamp and url in report', async () => {
+    mockSitemapNotFound(server, 'http://meta.local');
     server.use(
       http.get('http://meta.local/llms.txt', () => new HttpResponse(null, { status: 404 })),
       http.get('http://meta.local/docs/llms.txt', () => new HttpResponse(null, { status: 404 })),
@@ -456,6 +459,7 @@ describe('runner', () => {
   });
 
   it('includes discoverySources in report when page discovery runs', async () => {
+    mockSitemapNotFound(server, 'http://sources.local');
     server.use(
       http.get('http://sources.local/llms.txt', () =>
         HttpResponse.text('# Docs\n## Links\n- [A](http://sources.local/docs/a): A\n'),