diff --git a/src/upload_handler.mjs b/src/upload_handler.mjs
index 8dc9a74..d93ce02 100644
--- a/src/upload_handler.mjs
+++ b/src/upload_handler.mjs
@@ -601,7 +601,7 @@ export const handleUpload = async (req, res, self) => {
             // 4. Audio-only MP4 reclassification probe (only when needed)
             needsAudioMP4
                 ? (async () => {
-                    const origExt = file.filename.split('.').pop().toLowerCase();
+                    const origExt = file?.filename ? file.filename.split('.').pop().toLowerCase() : (inputUrl ? inputUrl.split('?')[0].split('.').pop().toLowerCase() : '');
                     if (['m4a', 'aac'].includes(origExt)) {
                         return 'audio/mp4'; // Extension-based reclassification
                     }