diff --git a/source/Ox/js/Type.js b/source/Ox/js/Type.js
index 651136ea..aee84d20 100644
--- a/source/Ox/js/Type.js
+++ b/source/Ox/js/Type.js
@@ -272,8 +272,9 @@ Ox.isPrimitive <f> Tests if a value is a primitive (boolean, number or string)
     false
 @*/
 Ox.isPrimitive = function(value) {
-    var type = Ox.typeOf(value);
-    return type == 'boolean' || type == 'number' || type == 'string';
+    return Ox.contains(
+        ['boolean', 'null', 'number', 'string', 'undefined'], Ox.typeOf(value)
+    );
 };
 
 /*@