diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Form/SettingsForm.php b/core/modules/aggregator/lib/Drupal/aggregator/Form/SettingsForm.php
index 6abd8d9..b830b1a 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Form/SettingsForm.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Form/SettingsForm.php
@@ -104,6 +104,8 @@ public function getFormID() {
    */
   protected function getConfigurableInstances() {
     if (!isset($this->configurableInstances)) {
+      $this->configurableInstances = array();
+
       $config = $this->configFactory->get('aggregator.settings');
 
       // Parse fetchers and parsers and collect their PluginFormInterface
@@ -243,7 +245,7 @@ public function getConfigNames() {
     $config_names = array('aggregator.settings');
 
     foreach ($this->getConfigurableInstances() as $instance) {
-      $config_names[] = $instance->getConfigNames();
+      $config_names += $instance->getConfigNames();
     }
 
     return array_unique($config_names);
diff --git a/core/modules/aggregator/tests/Drupal/aggregator/Tests/Form/SettingsFormTest.php b/core/modules/aggregator/tests/Drupal/aggregator/Tests/Form/SettingsFormTest.php
new file mode 100644
index 0000000..68c7d73
--- /dev/null
+++ b/core/modules/aggregator/tests/Drupal/aggregator/Tests/Form/SettingsFormTest.php
@@ -0,0 +1,122 @@
+<?php
+
+/**
+ * @file
+ * Contains\Drupal\aggregator\Tests\Form\SettingsFormTest.
+ */
+
+namespace Drupal\aggregator\Tests\Form;
+
+use Drupal\aggregator\Form\SettingsForm;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Tests \Drupal\aggregator\Form\SettingsForm.
+ */
+class SettingsFormTest extends UnitTestCase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getInfo() {
+    return array(
+      'name' => 'Aggregator settings form tests',
+      'description' => 'Unit tests for the aggregator settings form',
+      'group' => 'Aggregator',
+    );
+  }
+
+  public function setUp() {
+
+  }
+
+  /**
+   * Tests getConfigNames().
+   */
+  public function testGetConfigNames() {
+    // Test with no aggregator plugins.
+    $configs = array('aggregator.settings' => array());
+    $definitions = array();
+
+    list($settings_form) = $this->getSettingsForm($configs, $definitions);
+
+    $expected = array('aggregator.settings');
+    $this->assertSame($expected, $settings_form->getConfigNames());
+
+    // Test that aggregator plugins can add additional configuration names and
+    // that duplicated names are removed.
+    $configs = array('aggregator.settings' => array(
+      'fetcher' => 'aggregator_test_fetcher',
+      'parser' => 'aggregator_test_parser',
+      'processors' => array('aggregator_test_processor')
+    ));
+    $definitions = array(
+      'aggregator_test_fetcher' => array(
+        'title' => 'Test fetcher',
+        'description' => 'Test generic fetcher functionality.',
+      ),
+      'aggregator_test_parser' => array(
+        'title' => 'Test parser',
+        'description' => 'Test generic parser functionality.',
+      ),
+      'aggregator_test_processor' => array(
+        'title' => 'Test processor',
+        'description' => 'Test generic processor functionality.',
+      ),
+    );
+
+    list($settings_form, $plugin_manager) = $this->getSettingsForm($configs, $definitions);
+
+    $plugin = $this->getMock('Drupal\Core\Plugin\PluginFormInterface');
+    $plugin
+      ->expects($this->exactly(3))
+      ->method('getConfigNames')
+      ->will($this->returnValue(
+        array('aggregator.settings', 'aggregator_test.settings')
+      ));
+    $plugin_manager
+      ->expects($this->exactly(3))
+      ->method('createInstance')
+      ->will($this->returnValueMap(array(
+        array('aggregator_test_fetcher', array(), $plugin),
+        array('aggregator_test_parser', array(), $plugin),
+        array('aggregator_test_processor', array(), $plugin)
+      )));
+
+    $expected = array('aggregator.settings', 'aggregator_test.settings');
+
+    $this->assertSame($expected, $settings_form->getConfigNames());
+  }
+
+  /**
+   * Returns an aggregator settings form.
+   *
+   * @param array $configs
+   *   An array of configuration values as expected by
+   *   UnitTestCase::getConfigFactoryStub().
+   * @param array $definitions
+   *   An array of aggregator plugin definitions.
+   *
+   * @return array
+   *   An array that contains the aggregator settings form and mocked aggregator
+   *   plugin manager.
+   */
+  protected function getSettingsForm(array $configs, array $definitions) {
+    $plugin_manager = $this->getMockBuilder('Drupal\aggregator\Plugin\AggregatorPluginManager')
+      ->disableOriginalConstructor()
+      ->getMock();
+    $plugin_manager
+      ->expects($this->exactly(3))
+      ->method('getDefinitions')
+      ->will($this->returnValue($definitions));
+    return array(new SettingsForm(
+      $this->getConfigFactoryStub($configs),
+      $this->getMock('Drupal\Core\Config\Context\ContextInterface'),
+      $plugin_manager,
+      $plugin_manager,
+      $plugin_manager,
+      $this->getMock('Drupal\Core\StringTranslation\TranslationInterface')
+    ), $plugin_manager);
+  }
+
+}