diff --git a/proposed/PSR-Cache.md b/proposed/PSR-Cache.md
index 64791ca2a..1879ca1ef 100644
--- a/proposed/PSR-Cache.md
+++ b/proposed/PSR-Cache.md
@@ -118,6 +118,9 @@ namespace PSR\Cache;
  */
 interface Pool
 {
+
+    protected $prefix;
+
     /**
      * Returns objects which implement the Cache\Item interface.
      *
@@ -244,4 +247,4 @@ interface Item
      */
     function remove();
 }
-```
\ No newline at end of file
+```