diff --git a/packages/docusaurus-utils/src/vcs/__tests__/gitUtils.test.ts b/packages/docusaurus-utils/src/vcs/__tests__/gitUtils.test.ts
index 6a58c7d95b90..00b939c2b071 100644
--- a/packages/docusaurus-utils/src/vcs/__tests__/gitUtils.test.ts
+++ b/packages/docusaurus-utils/src/vcs/__tests__/gitUtils.test.ts
@@ -808,6 +808,23 @@ describe('VSC strategies', () => {
       });
     });
 
+    it('can read repo file info from a site-relative path', async () => {
+      const {vcs} = await initVsc();
+
+      // RouteMetadata.sourceFilePath is documented as relative to the site dir,
+      // and the sitemap plugin forwards it here unchanged. The map is keyed by
+      // absolute paths, so a relative path used to miss and silently return
+      // null, dropping <lastmod> from the sitemap.
+      await expect(vcs.getFileLastUpdateInfo('rootFile.md')).resolves.toEqual({
+        author: 'Seb',
+        timestamp: new Date('2020-06-19').getTime(),
+      });
+      await expect(vcs.getFileCreationInfo('rootFile.md')).resolves.toEqual({
+        author: 'Seb',
+        timestamp: new Date('2020-06-19').getTime(),
+      });
+    });
+
     it('can read submodule file', async () => {
       const {vcs, repoDir} = await initVsc();
 
diff --git a/packages/docusaurus-utils/src/vcs/vcsGitEager.ts b/packages/docusaurus-utils/src/vcs/vcsGitEager.ts
index c250877808c7..a505b485c1f9 100644
--- a/packages/docusaurus-utils/src/vcs/vcsGitEager.ts
+++ b/packages/docusaurus-utils/src/vcs/vcsGitEager.ts
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {resolve, basename} from 'node:path';
+import {resolve, basename, isAbsolute} from 'node:path';
 import logger, {PerfLogger} from '@docusaurus/logger';
 import {
   getGitAllRepoRoots,
@@ -82,11 +82,22 @@ async function initialize({
 
 export function createVcsGitEagerConfig(): VcsConfig {
   let initPromise: Promise<InitializeResult> | null = null;
+  let initSiteDir: string | null = null;
 
   async function getGitFileInfo(filePath: string): Promise<GitFileInfo | null> {
     const init = (await initPromise)!;
     if (init.type === 'success') {
-      return init.filesMap.get(filePath) ?? null;
+      // The map is keyed by absolute paths, but callers may pass a path
+      // relative to the site dir. RouteMetadata.sourceFilePath in particular
+      // "is expected to be relative to the site directory", which is what the
+      // sitemap plugin forwards here. The ad-hoc strategy tolerates both
+      // because it shells out to `git log`, so a relative path silently
+      // returned null here instead.
+      const key =
+        isAbsolute(filePath) || !initSiteDir
+          ? filePath
+          : resolve(initSiteDir, filePath);
+      return init.filesMap.get(key) ?? null;
     } else if (init.reason === 'not-in-worktree') {
       throw new Error(
         `This Docusaurus site is outside any Git worktree.
@@ -114,6 +125,7 @@ Unable to read Git info for file ${logger.path(filePath)} `,
         return;
       }
 
+      initSiteDir = siteDir;
       initPromise = PerfLogger.async('Git Eager VCS init', () =>
         initialize({siteDir}),
       );