1 files changed, 8 insertions, 1 deletions
diff --git a/Emby.Server.Implementations/Library/LibraryManager.cs b/Emby.Server.Implementations/Library/LibraryManager.cs
index 3691f4e19d..8d67f0c6c7 100644
--- a/Emby.Server.Implementations/Library/LibraryManager.cs
+++ b/Emby.Server.Implementations/Library/LibraryManager.cs
@@ -2315,9 +2315,16 @@ namespace Emby.Server.Implementations.Library
         {
             var comparer = Comparers.FirstOrDefault(c => name == c.Type);
 
-            // If it requires a user, create a new one, and assign the user
+            // User-dependent comparers (IUserBaseItemComparer) need a User. With no user
+            // (anonymous/API-key /Items requests), a user-dependent sort key is a caller contract
+            // violation — throw rather than silently falling back to a different key.
             if (comparer is IUserBaseItemComparer)
             {
+                if (user is null)
+                {
+                    throw new ArgumentException($"Sort key '{name}' requires a user, but none was provided.");
+                }
+
                 var userComparer = (IUserBaseItemComparer)Activator.CreateInstance(comparer.GetType())!; // only null for Nullable<T> instances
 
                 userComparer.User = user;