diff --git a/MediaBrowser.Providers/Subtitles/SubtitleManager.cs b/MediaBrowser.Providers/Subtitles/SubtitleManager.cs
index ae5e1090ad..420dd39a48 100644
--- a/MediaBrowser.Providers/Subtitles/SubtitleManager.cs
+++ b/MediaBrowser.Providers/Subtitles/SubtitleManager.cs
@@ -221,6 +221,11 @@ namespace MediaBrowser.Providers.Subtitles
 
         private async Task TrySaveToFiles(Stream stream, List<string> savePaths, Video video, string extension)
         {
+            if (!_allowedSubtitleFormats.Contains(extension, StringComparison.OrdinalIgnoreCase))
+            {
+                throw new ArgumentException($"Invalid subtitle format: {extension}");
+            }
+
             List<Exception>? exs = null;
 
             foreach (var savePath in savePaths)