diff --git a/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php
index e60c2f7df7..b3e4ef4d3e 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php
@@ -346,21 +346,22 @@ class XmlFileLoader extends FileLoader
                 $arg->setAttribute('key', $arg->getAttribute('name'));
             }
 
-            if (!$arg->hasAttribute('key')) {
-                $key = !$arguments ? 0 : max(array_keys($arguments)) + 1;
-            } else {
-                $key = $arg->getAttribute('key');
-            }
-
-            // parameter keys are case insensitive
-            if ('parameter' == $name && $lowercase) {
-                $key = strtolower($key);
-            }
-
             // this is used by DefinitionDecorator to overwrite a specific
             // argument of the parent definition
             if ($arg->hasAttribute('index')) {
                 $key = 'index_'.$arg->getAttribute('index');
+            } elseif (!$arg->hasAttribute('key')) {
+                // Append an empty argument, then fetch its key to overwrite it later
+                $arguments[] = null;
+                $keys = array_keys($arguments);
+                $key = array_pop($keys);
+            } else {
+                $key = $arg->getAttribute('key');
+
+                // parameter keys are case insensitive
+                if ('parameter' == $name && $lowercase) {
+                    $key = strtolower($key);
+                }
             }
 
             switch ($arg->getAttribute('type')) {
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/with_key_outside_collection.xml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/with_key_outside_collection.xml
new file mode 100644
index 0000000000..5f3a284361
--- /dev/null
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/with_key_outside_collection.xml
@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<container xmlns="http://symfony.com/schema/dic/services" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">
+  <services>
+    <service id="foo" class="Foo">
+      <argument key="type">foo</argument>
+      <argument>bar</argument>
+    </service>
+  </services>
+</container>
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php b/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php
index 2de5915f4e..fd45172284 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php
@@ -542,4 +542,13 @@ class XmlFileLoaderTest extends \PHPUnit_Framework_TestCase
         $this->assertSame('Baz', $barConfigurator[0]->getClass());
         $this->assertSame('configureBar', $barConfigurator[1]);
     }
+
+    public function testArgumentWithKeyOutsideCollection()
+    {
+        $container = new ContainerBuilder();
+        $loader = new XmlFileLoader($container, new FileLocator(self::$fixturesPath.'/xml'));
+        $loader->load('with_key_outside_collection.xml');
+
+        $this->assertSame(array('type' => 'foo', 'bar'), $container->getDefinition('foo')->getArguments());
+    }
 }