diff --git a/src/js/UI.js b/src/js/UI.js
index <HASH>..<HASH> 100644
--- a/src/js/UI.js
+++ b/src/js/UI.js
@@ -44,9 +44,7 @@ tabris.registerType("_UI", {
     image: "image",
     foreground: "color",
     background: "color",
-    activePage: function(value) {
-      return value instanceof tabris.Page;
-    }
+    activePage: true
   },
 
   _getProperty: {
Remove outdated and redundant check for "activePage" property

* The type is already checked in _setActivePage
* Functions are currently not supported as a value for _properties.
(They are treated like true - everything passes.)

Change-Id: I<I>ab3e0fd<I>ba7d1c8b3e7b<I>d2ca4f<I>