diff --git a/ox/movie.py b/ox/movie.py
index 23211ae..189fa3c 100644
--- a/ox/movie.py
+++ b/ox/movie.py
@@ -116,7 +116,7 @@ def parse_item_files(files):
         subtitle_files = [file for file in version_files[version_key] if file['extension'] == 'srt']
         for subtitle_language in sorted(
             list(set([file['language'] for file in subtitle_files])),
-            key=lambda x: LANGUAGES.index(x) if x in LANGUAGES else x
+            key=lambda x: '%d' % LANGUAGES.index(x) if x in LANGUAGES else x
         ):
             language_files = [file for file in subtitle_files if file['language'] == subtitle_language]
             if len(subtitle_files) == len(parts):