diff --git a/src/Jellyfin.Plugin.Dlna/Api/DlnaServerController.cs b/src/Jellyfin.Plugin.Dlna/Api/DlnaServerController.cs
index e814d37..99630c3 100644
--- a/src/Jellyfin.Plugin.Dlna/Api/DlnaServerController.cs
+++ b/src/Jellyfin.Plugin.Dlna/Api/DlnaServerController.cs
@@ -66,7 +66,12 @@ public ActionResult<string> GetDescriptionXml([FromRoute, Required] string serve
         string? userAgent = Request.Headers.UserAgent;
         if (userAgent is not null)
         {
-            userAgent = userAgent.Substring(0, userAgent.IndexOf('/'));
+            var firstIndexOfSlash = userAgent.IndexOf('/');
+            if (firstIndexOfSlash > 0)
+            {
+                userAgent = userAgent.Substring(0, firstIndexOfSlash);
+            }
+
             useRelativePath = _relativePathUserAgents.Contains(userAgent, StringComparison.Ordinal);
         }