diff --git a/backend/__tests__/routes/adminPhotoUploadSizeLimit.test.js b/backend/__tests__/routes/adminPhotoUploadSizeLimit.test.js
index 212d1b7e..51699068 100644
--- a/backend/__tests__/routes/adminPhotoUploadSizeLimit.test.js
+++ b/backend/__tests__/routes/adminPhotoUploadSizeLimit.test.js
@@ -63,10 +63,10 @@ describe('admin upload per-file size limit (general_max_file_size_mb)', () => {
     .set('Authorization', `Bearer ${adminToken}`)
     .attach('photos', Buffer.alloc(bytes, 0x41), { filename, contentType: 'image/jpeg' });
 
-  const postChunkedInit = (fileSize) => request(app)
+  const postChunkedInit = (fileSize, filename = 'clip.mp4') => request(app)
     .post(`/api/admin/photos/${eventId}/chunked-upload/init`)
     .set('Authorization', `Bearer ${adminToken}`)
-    .send({ filename: 'clip.mp4', fileSize, mimeType: 'video/mp4', totalChunks: 1 });
+    .send({ filename, fileSize, mimeType: 'video/mp4', totalChunks: 1 });
 
   beforeAll(async () => {
     ({ db, cleanup } = await bootCrmDb());
@@ -108,6 +108,20 @@ describe('admin upload per-file size limit (general_max_file_size_mb)', () => {
 
     uploadSettings = require('../../src/services/uploadSettings');
 
+    // chunked-upload/init now enforces the admin allow-list on the filename
+    // extension (the declared mimeType is ignored), exactly like the
+    // multipart path; the default list is images only, so admit mp4 here.
+    await db('app_settings')
+      .insert({
+        setting_key: 'general_allowed_file_types',
+        setting_value: JSON.stringify('jpg,jpeg,png,webp,mp4'),
+        setting_type: 'general',
+        updated_at: new Date().toISOString(),
+      })
+      .onConflict('setting_key')
+      .merge({ setting_value: JSON.stringify('jpg,jpeg,png,webp,mp4') });
+    uploadSettings.clearAllowedTypesCache();
+
     app = express();
     app.use(express.json());
     app.use('/api/admin/photos', require('../../src/routes/adminPhotos'));
@@ -129,6 +143,13 @@ describe('admin upload per-file size limit (general_max_file_size_mb)', () => {
     expect(res.body.error).toBe('File too large. Maximum size is 1 MB per file.');
   });
 
+  it('rejects a chunked upload whose extension is not on the allow-list, whatever MIME it declares', async () => {
+    await setLimitMb(50);
+    const res = await postChunkedInit(1024, 'page.html');
+    expect(res.status).toBe(400);
+    expect(res.body.error).toBe('File type not allowed');
+  });
+
   it('rejects chunk bytes over the limit regardless of the declared fileSize', async () => {
     await setLimitMb(1);
     const initRes = await postChunkedInit(1);
diff --git a/backend/src/routes/adminPhotos.js b/backend/src/routes/adminPhotos.js
index ee9064be..3194f7e8 100644
--- a/backend/src/routes/adminPhotos.js
+++ b/backend/src/routes/adminPhotos.js
@@ -1626,20 +1626,6 @@ router.post('/:eventId/chunked-upload/init', adminAuth, requirePermission('photo
       return res.status(400).json({ error: 'Missing required fields: filename, fileSize' });
     }
 
-    // The client-declared mimeType is not trusted. It used to be stored on
-    // the photo row verbatim and echoed as Content-Type by the gallery
-    // routes, so a JPEG/HTML polyglot declared as text/html rendered inline
-    // on the app origin. The MIME is derived from the extension instead,
-    // and the extension has to be on the admin's allow-list, which is what
-    // the multipart path enforces through its multer fileFilter.
-    const ext = path.extname(String(filename)).slice(1).toLowerCase();
-    const mimeType = Object.prototype.hasOwnProperty.call(EXTENSION_TO_MIME, ext)
-      ? EXTENSION_TO_MIME[ext]
-      : null;
-    const allowedMimeTypes = await getAllowedMimeTypes();
-    if (!mimeType || !allowedMimeTypes.includes(mimeType)) {
-      return res.status(400).json({ error: 'File type not allowed' });
-    }
 
     // Validate file size against the configured per-file cap. Hardcoding 10GB
     // here let the chunked path sidestep general_max_file_size_mb entirely.
@@ -1655,6 +1641,21 @@ router.post('/:eventId/chunked-upload/init', adminAuth, requirePermission('photo
       });
     }
 
+    // The client-declared mimeType is not trusted. It used to be stored on
+    // the photo row verbatim and echoed as Content-Type by the gallery
+    // routes, so a JPEG/HTML polyglot declared as text/html rendered inline
+    // on the app origin. The MIME is derived from the extension instead,
+    // and the extension has to be on the admin's allow-list, which is what
+    // the multipart path enforces through its multer fileFilter.
+    const ext = path.extname(String(filename)).slice(1).toLowerCase();
+    const mimeType = Object.prototype.hasOwnProperty.call(EXTENSION_TO_MIME, ext)
+      ? EXTENSION_TO_MIME[ext]
+      : null;
+    const allowedMimeTypes = await getAllowedMimeTypes();
+    if (!mimeType || !allowedMimeTypes.includes(mimeType)) {
+      return res.status(400).json({ error: 'File type not allowed' });
+    }
+
     const result = await chunkedUpload.initializeUpload({
       filename,
       fileSize,