diff --git a/src/Symfony/Component/Config/Definition/Builder/ArrayNodeDefinition.php b/src/Symfony/Component/Config/Definition/Builder/ArrayNodeDefinition.php
index 4717e5e2dd..28c93d49ce 100644
--- a/src/Symfony/Component/Config/Definition/Builder/ArrayNodeDefinition.php
+++ b/src/Symfony/Component/Config/Definition/Builder/ArrayNodeDefinition.php
@@ -103,7 +103,7 @@ class ArrayNodeDefinition extends NodeDefinition implements ParentNodeDefinition
     /**
      * Adds children with a default value when none are defined.
      *
-     * @param integer|string|array $children The number of children|The child name|The children names to be added
+     * @param integer|string|array|null $children The number of children|The child name|The children names to be added
      *
      * This method is applicable to prototype nodes only.
      *
@@ -111,7 +111,7 @@ class ArrayNodeDefinition extends NodeDefinition implements ParentNodeDefinition
      */
     public function addDefaultChildrenIfNoneSet($children = null)
     {
-        $this->addDefaultChildren = null === $children ? 'defaults' : $children;
+        $this->addDefaultChildren = $children;
 
         return $this;
     }
@@ -394,10 +394,24 @@ class ArrayNodeDefinition extends NodeDefinition implements ParentNodeDefinition
             );
         }
 
-        if ($this->default && false !== $this->addDefaultChildren) {
-            throw new InvalidDefinitionException(
-                sprintf('A default value and default children might not be used together at path "%s"', $path)
-            );
+        if (false !== $this->addDefaultChildren) {
+            if ($this->default) {
+                throw new InvalidDefinitionException(
+                    sprintf('A default value and default children might not be used together at path "%s"', $path)
+                );
+            }
+
+            if (null !== $this->key && (null === $this->addDefaultChildren || is_integer($this->addDefaultChildren) && $this->addDefaultChildren > 0)) {
+                throw new InvalidDefinitionException(
+                    sprintf('->addDefaultChildrenIfNoneSet() should set default children names as ->useAttributeAsKey() is used at path "%s"', $path)
+                );
+            }
+
+            if (null === $this->key && (is_string($this->addDefaultChildren) || is_array($this->addDefaultChildren))) {
+                throw new InvalidDefinitionException(
+                    sprintf('->addDefaultChildrenIfNoneSet() might not set default children names as ->useAttributeAsKey() is not used at path "%s"', $path)
+                );
+            }
         }
     }
 }
diff --git a/src/Symfony/Component/Config/Definition/PrototypedArrayNode.php b/src/Symfony/Component/Config/Definition/PrototypedArrayNode.php
index e8a52376ea..f800a3f8f5 100644
--- a/src/Symfony/Component/Config/Definition/PrototypedArrayNode.php
+++ b/src/Symfony/Component/Config/Definition/PrototypedArrayNode.php
@@ -124,11 +124,15 @@ class PrototypedArrayNode extends ArrayNode
     /**
      * Adds default children when none are set.
      *
-     * @param integer|string|array $children The number of children|The child name|The children names to be added
+     * @param integer|string|array|null $children The number of children|The child name|The children names to be added
      */
     public function setAddChildrenIfNoneSet($children = array('defaults'))
     {
-        $this->defaultChildren = is_integer($children) && $children > 0 ? range(1, $children) : (array) $children;
+        if (null === $children) {
+            $this->defaultChildren = array('defaults');
+        } else {
+            $this->defaultChildren = is_integer($children) && $children > 0 ? range(1, $children) : (array) $children;
+        }
     }
 
     /**
diff --git a/tests/Symfony/Tests/Component/Config/Definition/Builder/ArrayNodeDefinitionTest.php b/tests/Symfony/Tests/Component/Config/Definition/Builder/ArrayNodeDefinitionTest.php
index 93903c6302..b3495d4e44 100644
--- a/tests/Symfony/Tests/Component/Config/Definition/Builder/ArrayNodeDefinitionTest.php
+++ b/tests/Symfony/Tests/Component/Config/Definition/Builder/ArrayNodeDefinitionTest.php
@@ -13,6 +13,7 @@ namespace Symfony\Tests\Component\Config\Definition\Builder;
 
 use Symfony\Component\Config\Definition\Builder\ArrayNodeDefinition;
 use Symfony\Component\Config\Definition\Builder\ScalarNodeDefinition;
+use Symfony\Component\Config\Definition\Exception\InvalidDefinitionException;
 
 class ArrayNodeDefinitionTest extends \PHPUnit_Framework_TestCase
 {
@@ -21,7 +22,7 @@ class ArrayNodeDefinitionTest extends \PHPUnit_Framework_TestCase
         $parent = new ArrayNodeDefinition('root');
         $child = new ScalarNodeDefinition('child');
 
-        $node = $parent
+        $parent
             ->children()
                 ->scalarNode('foo')->end()
                 ->scalarNode('bar')->end()
@@ -79,7 +80,7 @@ class ArrayNodeDefinitionTest extends \PHPUnit_Framework_TestCase
         $node->getNode();
     }
 
-    public function testArrayNodeDefaultWhenUsingDefaultChildren()
+    public function testPrototypedArrayNodeDefaultWhenUsingDefaultChildren()
     {
         $node = new ArrayNodeDefinition('root');
         $node
@@ -90,6 +91,53 @@ class ArrayNodeDefinitionTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals(array(array()), $tree->getDefaultValue());
     }
 
+    /**
+     * @dataProvider providePrototypedArrayNodeDefaults
+     */
+    public function testPrototypedArrayNodeDefault($args, $shouldThrowWhenUsingAttrAsKey, $shouldThrowWhenNotUsingAttrAsKey, $defaults)
+    {
+        $node = new ArrayNodeDefinition('root');
+        $node
+            ->addDefaultChildrenIfNoneSet($args)
+            ->prototype('array')
+        ;
+
+        try {
+            $tree = $node->getNode();
+            $this->assertFalse($shouldThrowWhenNotUsingAttrAsKey);
+            $this->assertEquals($defaults, $tree->getDefaultValue());
+        } catch (InvalidDefinitionException $e) {
+            $this->assertTrue($shouldThrowWhenNotUsingAttrAsKey);
+        }
+
+        $node = new ArrayNodeDefinition('root');
+        $node
+            ->useAttributeAsKey('attr')
+            ->addDefaultChildrenIfNoneSet($args)
+            ->prototype('array')
+        ;
+
+        try {
+            $tree = $node->getNode();
+            $this->assertFalse($shouldThrowWhenUsingAttrAsKey);
+            $this->assertEquals($defaults, $tree->getDefaultValue());
+        } catch (InvalidDefinitionException $e) {
+            $this->assertTrue($shouldThrowWhenUsingAttrAsKey);
+        }
+    }
+
+    public function providePrototypedArrayNodeDefaults()
+    {
+        return array(
+            array(null, true, false, array(array())),
+            array(2, true, false, array(array(), array())),
+            array('2', false, true, array('2' => array())),
+            array('foo', false, true, array('foo' => array())),
+            array(array('foo'), false, true, array('foo' => array())),
+            array(array('foo', 'bar'), false, true, array('foo' => array(), 'bar' => array())),
+        );
+    }
+
     public function testNestedPrototypedArrayNodes()
     {
         $node = new ArrayNodeDefinition('root');
@@ -98,7 +146,7 @@ class ArrayNodeDefinitionTest extends \PHPUnit_Framework_TestCase
             ->prototype('array')
                   ->prototype('array')
         ;
-        $tree = $node->getNode();
+        $node->getNode();
     }
 
     protected function getField($object, $field)