diff --git a/web/src/torrent.js b/web/src/torrent.js
index d155420ce..a496e98be 100644
--- a/web/src/torrent.js
+++ b/web/src/torrent.js
@@ -200,7 +200,7 @@ export class Torrent extends EventTarget {
     return this.fields.pieceSize;
   }
   getPrimaryMimeType() {
-    return this.fields['primary-mime-type'];
+    return this.fields['primary-mime-type'] || 'application/octet-stream';
   }
   getPrivateFlag() {
     return this.fields.isPrivate;