diff --git a/tubetube/yt_downloader.py b/tubetube/yt_downloader.py
index 8740952..7277c53 100644
--- a/tubetube/yt_downloader.py
+++ b/tubetube/yt_downloader.py
@@ -185,7 +185,7 @@ def _download_item(self, download_id):
             "no_overwrites": True,
             "verbose": self.verbose_ytdlp,
             "no_mtime": True,
-            "format_sort": "vcodec:vp9,vext:mp4,size,acodec:aac",
+            "format_sort": ["vcodec:vp9", "vext:mp4", "size", "acodec:aac"],
         }
 
         post_processors = [