diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 0026cb0..111e89a 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -296,12 +296,12 @@ abstract class DrupalCacheArray implements ArrayAccess {
   /**
    * A cid to pass to cache()->set() and cache()->get().
    */
-  protected $cid;
+  private $cid;
 
   /**
    * A bin to pass to cache()->set() and cache()->get().
    */
-  protected $bin;
+  private $bin;
 
   /**
    * An array of keys to add to the cache at the end of the request.