diff --git a/Jellyfin.Plugin.SmartPlaylist/Lisp/Interpreter.cs b/Jellyfin.Plugin.SmartPlaylist/Lisp/Interpreter.cs
index d16f46d..8cc0225 100644
--- a/Jellyfin.Plugin.SmartPlaylist/Lisp/Interpreter.cs
+++ b/Jellyfin.Plugin.SmartPlaylist/Lisp/Interpreter.cs
@@ -74,6 +74,13 @@ namespace Jellyfin.Plugin.SmartPlaylist.Lisp {
                       (cons (cons (car lst) (car s)) (cdr s)))))
                 """
             );
+            this["length"] = e.eval(
+                """
+                (lambda
+                  (lst n)
+                  (if (null lst) n (length (cdr lst) (+ n 1))))
+                """
+            );
             this["qsort"] = e.eval(
                 """
                 (lambda