diff --git a/Foundation/CPAttributedString.j b/Foundation/CPAttributedString.j
index 15a7c27687..01940912a3 100644
--- a/Foundation/CPAttributedString.j
+++ b/Foundation/CPAttributedString.j
@@ -655,7 +655,7 @@
     @param anIndex the index at which the insert is to occur.
     @exception CPRangeException If the index is out of bounds.
 */
-- (void)insertAttributedString:(CPAttributedString)aString atIndex:(CPString)anIndex
+- (void)insertAttributedString:(CPAttributedString)aString atIndex:(unsigned)anIndex
 {
     [self beginEditing];
 
@@ -828,3 +828,4 @@ var splitRangeEntry = function splitRangeEntryAtIndex(/*RangeEntry*/aRangeEntry,
     
     return [aRangeEntry, newRangeEntry];
 }
+