diff --git a/backend/cover.py b/backend/cover.py
index 89465e2..4432a52 100644
--- a/backend/cover.py
+++ b/backend/cover.py
@@ -33,12 +33,14 @@ def download(url: str, album_path: Path) -> None:
     '''General cover art downloader'''
 
     resp = http_pool.get().request('GET', url)
-    ext = mimetypes.guess_extension(resp.headers['content-type']) or '.jpg'
+    ct = resp.headers['content-type']
+    if not ct.startswith('image'):
+        raise ValueError('thumbnail is not an image')
+    ext = mimetypes.guess_extension(ct) or '.jpg'
 
     path = album_path / ('cover' + ext)
     if path.exists():
         return
 
-    with (album_path / ('cover' + ext)).open('wb') as f:
-        for chunk in resp.read_chunked():
-            f.write(chunk)
+    with path.open('wb') as f:
+        f.write(resp.data)