diff --git a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
index e7703aabf89a9..d84112d527316 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
@@ -205,7 +205,7 @@ private function parseDefinitions(array $content, $file)
             throw new InvalidArgumentException(sprintf('The "services" key should contain an array in %s. Check your YAML syntax.', $file));
         }
 
-        if (isset($content['services']['_instanceof'])) {
+        if (array_key_exists('_instanceof', $content['services'])) {
             $instanceof = $content['services']['_instanceof'];
             unset($content['services']['_instanceof']);
 
@@ -242,7 +242,7 @@ private function parseDefinitions(array $content, $file)
      */
     private function parseDefaults(array &$content, $file)
     {
-        if (!isset($content['services']['_defaults'])) {
+        if (!array_key_exists('_defaults', $content['services'])) {
             return array();
         }
         $defaults = $content['services']['_defaults'];
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/bad_empty_defaults.yml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/bad_empty_defaults.yml
new file mode 100644
index 0000000000000..85d910e3e31fb
--- /dev/null
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/bad_empty_defaults.yml
@@ -0,0 +1,2 @@
+services:
+    _defaults:
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/bad_empty_instanceof.yml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/bad_empty_instanceof.yml
new file mode 100644
index 0000000000000..2c8ce09ff6f3e
--- /dev/null
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/yaml/bad_empty_instanceof.yml
@@ -0,0 +1,2 @@
+services:
+    _instanceof:
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php b/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
index 87a05eb2abd1f..a87619e03287b 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
@@ -577,6 +577,28 @@ public function testAutoConfigureInstanceof()
         $this->assertTrue($container->getDefinition('use_defaults_settings')->isAutoconfigured());
         $this->assertFalse($container->getDefinition('override_defaults_settings_to_false')->isAutoconfigured());
     }
+
+    /**
+     * @expectedException \Symfony\Component\DependencyInjection\Exception\InvalidArgumentException
+     * @expectedExceptionMessage Service "_defaults" key must be an array, "NULL" given in "bad_empty_defaults.yml".
+     */
+    public function testEmptyDefaultsThrowsClearException()
+    {
+        $container = new ContainerBuilder();
+        $loader = new YamlFileLoader($container, new FileLocator(self::$fixturesPath.'/yaml'));
+        $loader->load('bad_empty_defaults.yml');
+    }
+
+    /**
+     * @expectedException \Symfony\Component\DependencyInjection\Exception\InvalidArgumentException
+     * @expectedExceptionMessage Service "_instanceof" key must be an array, "NULL" given in "bad_empty_instanceof.yml".
+     */
+    public function testEmptyInstanceofThrowsClearException()
+    {
+        $container = new ContainerBuilder();
+        $loader = new YamlFileLoader($container, new FileLocator(self::$fixturesPath.'/yaml'));
+        $loader->load('bad_empty_instanceof.yml');
+    }
 }
 
 interface FooInterface