diff --git a/src/Symfony/Component/Form/FormConfigBuilder.php b/src/Symfony/Component/Form/FormConfigBuilder.php
index bbe1914dec8b8..d217cf019365d 100644
--- a/src/Symfony/Component/Form/FormConfigBuilder.php
+++ b/src/Symfony/Component/Form/FormConfigBuilder.php
@@ -854,6 +854,10 @@ public function setRequestHandler(RequestHandlerInterface $requestHandler)
      */
     public function setAutoInitialize($initialize)
     {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
         $this->autoInitialize = (bool) $initialize;
 
         return $this;