diff --git a/src/Symfony/Component/HttpFoundation/Session/Storage/MockFileSessionStorage.php b/src/Symfony/Component/HttpFoundation/Session/Storage/MockFileSessionStorage.php
index 56e6513800..5bf2962ae6 100644
--- a/src/Symfony/Component/HttpFoundation/Session/Storage/MockFileSessionStorage.php
+++ b/src/Symfony/Component/HttpFoundation/Session/Storage/MockFileSessionStorage.php
@@ -29,6 +29,8 @@ class MockFileSessionStorage extends MockArraySessionStorage
      */
     private $savePath;
 
+    private $sessionData;
+
     /**
      * Constructor.
      *