diff --git a/Foundation/CPAttributedString.j b/Foundation/CPAttributedString.j
index 5a24d0ce1..7c0a14055 100644
--- a/Foundation/CPAttributedString.j
+++ b/Foundation/CPAttributedString.j
@@ -558,6 +558,9 @@ import <Foundation/CPString.j>
 
 @end
 
+@implementation CPMutableAttributedString : CPAttributedString {}
+@end
+
 var isEqual = function isEqual(a, b)
 {
     if (a == b)