diff --git a/UPGRADE-3.4.md b/UPGRADE-3.4.md
index 1b9a40c452..0119ca02f5 100644
--- a/UPGRADE-3.4.md
+++ b/UPGRADE-3.4.md
@@ -1,6 +1,11 @@
 UPGRADE FROM 3.3 to 3.4
 =======================
 
+Config
+------
+
+ * Using protected builder property of TreeBuilder is deprecated and property will be removed in 4.0.
+
 DependencyInjection
 -------------------
 
diff --git a/src/Symfony/Component/Config/Definition/Builder/TreeBuilder.php b/src/Symfony/Component/Config/Definition/Builder/TreeBuilder.php
index 5d02848a09..384477c501 100644
--- a/src/Symfony/Component/Config/Definition/Builder/TreeBuilder.php
+++ b/src/Symfony/Component/Config/Definition/Builder/TreeBuilder.php
@@ -22,6 +22,10 @@ class TreeBuilder implements NodeParentInterface
 {
     protected $tree;
     protected $root;
+
+    /**
+     * @deprecated since 3.4. To be removed in 4.0
+     */
     protected $builder;
 
     /**