diff --git a/UPGRADE-2.2.md b/UPGRADE-2.2.md
index 8dc849d513..a14fdda35b 100644
--- a/UPGRADE-2.2.md
+++ b/UPGRADE-2.2.md
@@ -57,6 +57,13 @@
 
  * The PasswordType is now not trimmed by default.
 
+ * The class FormException is now an interface. The old class is still available
+   under the name Symfony\Component\Form\Exception\Exception, but will probably
+   be removed before 2.2. If you created FormException instances manually,
+   you are now advised to create any of the other exceptions in the
+   Symfony\Component\Form\Exception namespace or to create custom exception
+   classes for your purpose.
+
 #### Deprecations
 
  * The methods `getParent()`, `setParent()` and `hasParent()` in
diff --git a/src/Symfony/Component/Form/CHANGELOG.md b/src/Symfony/Component/Form/CHANGELOG.md
index d0d298f9df..c229302a5e 100644
--- a/src/Symfony/Component/Form/CHANGELOG.md
+++ b/src/Symfony/Component/Form/CHANGELOG.md
@@ -10,6 +10,8 @@ CHANGELOG
  * removed special characters between the choice or text fields of DateType unless
    the option "format" is set to a custom value
  * deprecated FormException and introduced ExceptionInterface instead
+ * [BC BREAK] FormException is now an interface
+ * protected FormBuilder methods from being called when it is turned into a FormConfigInterface with getFormConfig()
 
 2.1.0
 -----
diff --git a/src/Symfony/Component/Form/Exception/BadMethodCallException.php b/src/Symfony/Component/Form/Exception/BadMethodCallException.php
new file mode 100644
index 0000000000..27649dd022
--- /dev/null
+++ b/src/Symfony/Component/Form/Exception/BadMethodCallException.php
@@ -0,0 +1,21 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Form\Exception;
+
+/**
+ * Base BadMethodCallException for the Form component.
+ *
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ */
+class BadMethodCallException extends \BadMethodCallException implements ExceptionInterface
+{
+}
diff --git a/src/Symfony/Component/Form/FormBuilder.php b/src/Symfony/Component/Form/FormBuilder.php
index 428044e21a..0cec9b9426 100644
--- a/src/Symfony/Component/Form/FormBuilder.php
+++ b/src/Symfony/Component/Form/FormBuilder.php
@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\Form;
 
+use Symfony\Component\Form\Exception\BadMethodCallException;
 use Symfony\Component\Form\Exception\Exception;
 use Symfony\Component\Form\Exception\UnexpectedTypeException;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
@@ -65,7 +66,7 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
     public function add($child, $type = null, array $options = array())
     {
         if ($this->locked) {
-            throw new Exception('The form builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         if ($child instanceof self) {
@@ -102,7 +103,7 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
     public function create($name, $type = null, array $options = array())
     {
         if ($this->locked) {
-            throw new Exception('The form builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         if (null === $type && null === $this->getDataClass()) {
@@ -121,6 +122,10 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
      */
     public function get($name)
     {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
         if (isset($this->unresolvedChildren[$name])) {
             return $this->resolveChild($name);
         }
@@ -138,7 +143,7 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
     public function remove($name)
     {
         if ($this->locked) {
-            throw new Exception('The form builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         unset($this->unresolvedChildren[$name]);
@@ -158,6 +163,10 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
      */
     public function has($name)
     {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
         if (isset($this->unresolvedChildren[$name])) {
             return true;
         }
@@ -174,6 +183,10 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
      */
     public function all()
     {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
         $this->resolveChildren();
 
         return $this->children;
@@ -184,6 +197,10 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
      */
     public function count()
     {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
         return count($this->children);
     }
 
@@ -192,6 +209,10 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
      */
     public function getForm()
     {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
         $this->resolveChildren();
 
         $form = new Form($this->getFormConfig());
@@ -208,6 +229,10 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
      */
     public function getParent()
     {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
         return $this->parent;
     }
 
@@ -217,7 +242,7 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
     public function setParent(FormBuilderInterface $parent = null)
     {
         if ($this->locked) {
-            throw new Exception('The form builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->parent = $parent;
@@ -230,9 +255,53 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
      */
     public function hasParent()
     {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
         return null !== $this->parent;
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public function getIterator()
+    {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
+        return new \ArrayIterator($this->children);
+    }
+
+    /**
+     * Returns the types used by this builder.
+     *
+     * @return FormTypeInterface[] An array of FormTypeInterface
+     *
+     * @deprecated Deprecated since version 2.1, to be removed in 2.3. Use
+     *             {@link FormConfigInterface::getType()} instead.
+     *
+     * @throws BadMethodCallException If the builder was turned into a {@link FormConfigInterface}
+     *                                via {@link getFormConfig()}.
+     */
+    public function getTypes()
+    {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
+        trigger_error('getTypes() is deprecated since version 2.1 and will be removed in 2.3. Use getConfig() and FormConfigInterface::getType() instead.', E_USER_DEPRECATED);
+
+        $types = array();
+
+        for ($type = $this->getType(); null !== $type; $type = $type->getParent()) {
+            array_unshift($types, $type->getInnerType());
+        }
+
+        return $types;
+    }
+
     /**
      * Converts an unresolved child into a {@link FormBuilder} instance.
      *
@@ -261,33 +330,4 @@ class FormBuilder extends FormConfigBuilder implements \IteratorAggregate, FormB
 
         $this->unresolvedChildren = array();
     }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function getIterator()
-    {
-        return new \ArrayIterator($this->children);
-    }
-
-    /**
-     * Returns the types used by this builder.
-     *
-     * @return FormTypeInterface[] An array of FormTypeInterface
-     *
-     * @deprecated Deprecated since version 2.1, to be removed in 2.3. Use
-     *             {@link FormConfigInterface::getType()} instead.
-     */
-    public function getTypes()
-    {
-        trigger_error('getTypes() is deprecated since version 2.1 and will be removed in 2.3. Use getConfig() and FormConfigInterface::getType() instead.', E_USER_DEPRECATED);
-
-        $types = array();
-
-        for ($type = $this->getType(); null !== $type; $type = $type->getParent()) {
-            array_unshift($types, $type->getInnerType());
-        }
-
-        return $types;
-    }
 }
diff --git a/src/Symfony/Component/Form/FormConfigBuilder.php b/src/Symfony/Component/Form/FormConfigBuilder.php
index 942e3346f4..1b428194f8 100644
--- a/src/Symfony/Component/Form/FormConfigBuilder.php
+++ b/src/Symfony/Component/Form/FormConfigBuilder.php
@@ -11,6 +11,7 @@
 
 namespace Symfony\Component\Form;
 
+use Symfony\Component\Form\Exception\BadMethodCallException;
 use Symfony\Component\Form\Exception\Exception;
 use Symfony\Component\Form\Exception\UnexpectedTypeException;
 use Symfony\Component\Form\Util\PropertyPath;
@@ -172,7 +173,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function addEventListener($eventName, $listener, $priority = 0)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->dispatcher->addListener($eventName, $listener, $priority);
@@ -186,7 +187,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function addEventSubscriber(EventSubscriberInterface $subscriber)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->dispatcher->addSubscriber($subscriber);
@@ -202,7 +203,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
         trigger_error('addValidator() is deprecated since version 2.1 and will be removed in 2.3.', E_USER_DEPRECATED);
 
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->validators[] = $validator;
@@ -216,7 +217,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function addViewTransformer(DataTransformerInterface $viewTransformer, $forcePrepend = false)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         if ($forcePrepend) {
@@ -234,7 +235,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function resetViewTransformers()
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->viewTransformers = array();
@@ -249,7 +250,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      *
      * @return FormConfigBuilder The configuration object.
      *
-     * @throws Exception if the form configuration is locked
+     * @throws BadMethodCallException if the form configuration is locked
      *
      * @deprecated Deprecated since version 2.1, to be removed in 2.3. Use
      *             {@link addViewTransformer()} instead.
@@ -259,7 +260,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
         trigger_error('appendClientTransformer() is deprecated since version 2.1 and will be removed in 2.3. Use addViewTransformer() instead.', E_USER_DEPRECATED);
 
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         return $this->addViewTransformer($viewTransformer);
@@ -272,7 +273,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      *
      * @return FormConfigBuilder The configuration object.
      *
-     * @throws Exception if the form configuration is locked
+     * @throws BadMethodCallException if the form configuration is locked
      *
      * @deprecated Deprecated since version 2.1, to be removed in 2.3.
      */
@@ -281,7 +282,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
         trigger_error('prependClientTransformer() is deprecated since version 2.1 and will be removed in 2.3.', E_USER_DEPRECATED);
 
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         return $this->addViewTransformer($viewTransformer, true);
@@ -292,7 +293,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      *
      * @return FormConfigBuilder The configuration object.
      *
-     * @throws Exception if the form configuration is locked
+     * @throws BadMethodCallException if the form configuration is locked
      *
      * @deprecated Deprecated since version 2.1, to be removed in 2.3. Use
      *             {@link resetViewTransformers()} instead.
@@ -302,7 +303,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
         trigger_error('resetClientTransformers() is deprecated since version 2.1 and will be removed in 2.3. Use resetViewTransformers() instead.', E_USER_DEPRECATED);
 
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         return $this->resetViewTransformers();
@@ -314,7 +315,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function addModelTransformer(DataTransformerInterface $modelTransformer, $forceAppend = false)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         if ($forceAppend) {
@@ -332,7 +333,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function resetModelTransformers()
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->modelTransformers = array();
@@ -347,7 +348,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      *
      * @return FormConfigBuilder The configuration object.
      *
-     * @throws Exception if the form configuration is locked
+     * @throws BadMethodCallException if the form configuration is locked
      *
      * @deprecated Deprecated since version 2.1, to be removed in 2.3.
      */
@@ -356,7 +357,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
         trigger_error('appendNormTransformer() is deprecated since version 2.1 and will be removed in 2.3.', E_USER_DEPRECATED);
 
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         return $this->addModelTransformer($modelTransformer, true);
@@ -369,7 +370,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      *
      * @return FormConfigBuilder The configuration object.
      *
-     * @throws Exception if the form configuration is locked
+     * @throws BadMethodCallException if the form configuration is locked
      *
      * @deprecated Deprecated since version 2.1, to be removed in 2.3. Use
      *             {@link addModelTransformer()} instead.
@@ -379,7 +380,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
         trigger_error('prependNormTransformer() is deprecated since version 2.1 and will be removed in 2.3. Use addModelTransformer() instead.', E_USER_DEPRECATED);
 
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         return $this->addModelTransformer($modelTransformer);
@@ -390,7 +391,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      *
      * @return FormConfigBuilder The configuration object.
      *
-     * @throws Exception if the form configuration is locked
+     * @throws BadMethodCallException if the form configuration is locked
      *
      * @deprecated Deprecated since version 2.1, to be removed in 2.3. Use
      *             {@link resetModelTransformers()} instead.
@@ -400,7 +401,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
         trigger_error('resetNormTransformers() is deprecated since version 2.1 and will be removed in 2.3. Use resetModelTransformers() instead.', E_USER_DEPRECATED);
 
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         return $this->resetModelTransformers();
@@ -652,7 +653,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setAttribute($name, $value)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->attributes[$name] = $value;
@@ -666,7 +667,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setAttributes(array $attributes)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->attributes = $attributes;
@@ -680,7 +681,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setDataMapper(DataMapperInterface $dataMapper = null)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->dataMapper = $dataMapper;
@@ -694,7 +695,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setDisabled($disabled)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->disabled = (Boolean) $disabled;
@@ -708,7 +709,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setEmptyData($emptyData)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->emptyData = $emptyData;
@@ -722,7 +723,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setErrorBubbling($errorBubbling)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->errorBubbling = null === $errorBubbling ? null : (Boolean) $errorBubbling;
@@ -736,7 +737,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setRequired($required)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->required = (Boolean) $required;
@@ -750,7 +751,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setPropertyPath($propertyPath)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         if (null !== $propertyPath && !$propertyPath instanceof PropertyPathInterface) {
@@ -768,7 +769,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setMapped($mapped)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->mapped = $mapped;
@@ -782,7 +783,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setByReference($byReference)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->byReference = $byReference;
@@ -796,7 +797,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setVirtual($virtual)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->virtual = $virtual;
@@ -810,7 +811,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setCompound($compound)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->compound = $compound;
@@ -824,7 +825,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setType(ResolvedFormTypeInterface $type)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->type = $type;
@@ -838,7 +839,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setData($data)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->data = $data;
@@ -852,7 +853,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setDataLocked($locked)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->dataLocked = $locked;
@@ -866,7 +867,7 @@ class FormConfigBuilder implements FormConfigBuilderInterface
     public function setFormFactory(FormFactoryInterface $formFactory)
     {
         if ($this->locked) {
-            throw new Exception('The config builder cannot be modified anymore.');
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
         }
 
         $this->formFactory = $formFactory;
@@ -879,6 +880,10 @@ class FormConfigBuilder implements FormConfigBuilderInterface
      */
     public function getFormConfig()
     {
+        if ($this->locked) {
+            throw new BadMethodCallException('FormConfigBuilder methods cannot be accessed anymore once the builder is turned into a FormConfigInterface instance.');
+        }
+
         // This method should be idempotent, so clone the builder
         $config = clone $this;
         $config->locked = true;