diff --git a/lib/Cake/bootstrap.php b/lib/Cake/bootstrap.php
index 443653f9d..08cb5d2ea 100644
--- a/lib/Cake/bootstrap.php
+++ b/lib/Cake/bootstrap.php
@@ -141,6 +141,11 @@ App::$bootstrapping = true;
 
 Configure::bootstrap(isset($boot) ? $boot : true);
 
+/**
+ * Compatibility with 2.1, which expects Set to always be autoloaded.
+ */
+App::uses('Set', 'Utilty');
+
 /**
  *  Full url prefix
  */