diff --git a/Foundation/Boxing.swift b/Foundation/Boxing.swift
index 752f581..4fe7346 100644
--- a/Foundation/Boxing.swift
+++ b/Foundation/Boxing.swift
@@ -14,7 +14,7 @@
 ///
 /// Note: This assumes that the result of calling copy() is mutable. The documentation says that classes which do not have a mutable/immutable distinction should just adopt NSCopying instead of NSMutableCopying.
 internal final class _MutableHandle<MutableType : NSObject> where MutableType : NSCopying {
-    fileprivate var _pointer : MutableType
+    @_versioned internal var _pointer : MutableType
     
     init(reference : MutableType) {
         _pointer = reference.copy() as! MutableType