diff --git a/.changeset/public-spoons-find.md b/.changeset/public-spoons-find.md
new file mode 100644
index 00000000000..f3a1be539c2
--- /dev/null
+++ b/.changeset/public-spoons-find.md
@@ -0,0 +1,8 @@
+---
+'@tanstack/start-plugin-core': patch
+'@tanstack/react-start': patch
+'@tanstack/solid-start': patch
+'@tanstack/vue-start': patch
+---
+
+fix: add `xmlns:xhtml` to generated sitemap
diff --git a/packages/start-plugin-core/src/build-sitemap.ts b/packages/start-plugin-core/src/build-sitemap.ts
index fabb9f19d27..3eae17ca021 100644
--- a/packages/start-plugin-core/src/build-sitemap.ts
+++ b/packages/start-plugin-core/src/build-sitemap.ts
@@ -203,6 +203,7 @@ function createXml(elementName: 'urlset' | 'sitemapindex'): XMLBuilder {
   return create({ version: '1.0', encoding: 'UTF-8' })
     .ele(elementName, {
       xmlns: 'https://www.sitemaps.org/schemas/sitemap/0.9',
+      'xmlns:xhtml': 'http://www.w3.org/1999/xhtml',
     })
     .com(`This file was automatically generated by TanStack Start.`)
 }