diff --git a/core/lib/Drupal/Core/Form/ConfigFormBase.php b/core/lib/Drupal/Core/Form/ConfigFormBase.php
index d310dc1..704e443 100644
--- a/core/lib/Drupal/Core/Form/ConfigFormBase.php
+++ b/core/lib/Drupal/Core/Form/ConfigFormBase.php
@@ -15,7 +15,7 @@
 /**
  * Base class for implementing system configuration forms.
  */
-abstract class ConfigFormBase extends FormBase implements ConfigFormInterface {
+abstract class ConfigFormBase extends FormBase implements FormInterface, ConfigFormInterface {
   use ConfigFormBaseTrait;
 
   /**
diff --git a/core/lib/Drupal/Core/Form/ConfigFormInterface.php b/core/lib/Drupal/Core/Form/ConfigFormInterface.php
index 08335fe..4d117d3 100644
--- a/core/lib/Drupal/Core/Form/ConfigFormInterface.php
+++ b/core/lib/Drupal/Core/Form/ConfigFormInterface.php
@@ -7,9 +7,7 @@
 
 namespace Drupal\Core\Form;
 
-use Drupal\Core\Form\FormInterface;
-
-interface ConfigFormInterface extends FormInterface {
+interface ConfigFormInterface {
 
   /**
    * Returns an array of configuration that are edited as part of the form.
diff --git a/core/lib/Drupal/Core/Form/PluginConfigFormInterface.php b/core/lib/Drupal/Core/Form/PluginConfigFormInterface.php
deleted file mode 100644
index 1e9d2cb..0000000
--- a/core/lib/Drupal/Core/Form/PluginConfigFormInterface.php
+++ /dev/null
@@ -1,22 +0,0 @@
-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\Form\PluginConfigFormInterface.
- */
-
-namespace Drupal\Core\Form;
-
-use Drupal\Core\Form\FormInterface;
-
-interface PluginConfigFormInterface extends FormInterface {
-
-  /**
-   * Returns an array of configuration that are edited as part of the form.
-   *
-   * @return array
-   *   An array of editable configuration names.
-   */
-  public function getEditableConfigNames();
-
-}
diff --git a/core/modules/aggregator/src/Form/SettingsForm.php b/core/modules/aggregator/src/Form/SettingsForm.php
index bff3222..7842599 100644
--- a/core/modules/aggregator/src/Form/SettingsForm.php
+++ b/core/modules/aggregator/src/Form/SettingsForm.php
@@ -10,7 +10,7 @@
 use Drupal\aggregator\Plugin\AggregatorPluginManager;
 use Drupal\Component\Utility\String;
 use Drupal\Core\Config\ConfigFactoryInterface;
-use Drupal\Core\Form\PluginConfigFormInterface;
+use Drupal\Core\Form\ConfigFormInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\PluginFormInterface;
 use Drupal\Core\StringTranslation\TranslationInterface;
@@ -104,7 +104,7 @@ public function getEditableConfigNames() {
     $config_names = ['aggregator.settings'];
 
     foreach ($this->getConfigurableInstances() as $instance) {
-      if ($instance instanceof \Drupal\Core\Form\PluginConfigFormInterface) {
+      if ($instance instanceof ConfigFormInterface) {
         $config_names = array_merge($config_names, $instance->getEditableConfigNames());
       }
     }
diff --git a/core/modules/aggregator/src/Plugin/AggregatorPluginSettingsBase.php b/core/modules/aggregator/src/Plugin/AggregatorPluginSettingsBase.php
index 5495b25..6803a2f 100644
--- a/core/modules/aggregator/src/Plugin/AggregatorPluginSettingsBase.php
+++ b/core/modules/aggregator/src/Plugin/AggregatorPluginSettingsBase.php
@@ -8,9 +8,10 @@
 namespace Drupal\aggregator\Plugin;
 
 use Drupal\Component\Plugin\ConfigurablePluginInterface;
-use Drupal\Core\Form\PluginConfigFormInterface;
+use Drupal\Core\Form\ConfigFormInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\PluginBase;
+use Drupal\Core\Plugin\PluginFormInterface;
 
 /**
  * Base class for aggregator plugins that implement settings forms.
@@ -24,7 +25,7 @@
  * @see \Drupal\aggregator\Plugin\ParserInterface
  * @see plugin_api
  */
-abstract class AggregatorPluginSettingsBase extends PluginBase implements PluginConfigFormInterface, ConfigurablePluginInterface {
+abstract class AggregatorPluginSettingsBase extends PluginBase implements PluginFormInterface, ConfigurablePluginInterface, ConfigFormInterface {
 
   /**
    * {@inheritdoc}
diff --git a/core/modules/aggregator/tests/src/Unit/Form/SettingsFormTest.php b/core/modules/aggregator/tests/src/Unit/Form/SettingsFormTest.php
index 2491c66..6053db0 100644
--- a/core/modules/aggregator/tests/src/Unit/Form/SettingsFormTest.php
+++ b/core/modules/aggregator/tests/src/Unit/Form/SettingsFormTest.php
@@ -5,13 +5,15 @@
  * Contains \Drupal\aggregator\Tests\Form\SettingsFormTest.
  */
 
-namespace Drupal\aggregator\Tests\Form;
+namespace Drupal\Tests\aggregator\Unit\Form;
 
 use Drupal\aggregator\Form\SettingsForm;
 use Drupal\Tests\UnitTestCase;
 
 /**
  * Tests \Drupal\aggregator\Form\SettingsForm.
+ *
+ * @group aggregator
  */
 class SettingsFormTest extends UnitTestCase {
 
@@ -96,7 +98,6 @@ protected function getSettingsForm(array $configs, array $definitions, array $co
 
     $settings_form = new SettingsForm(
       $this->getConfigFactoryStub($configs),
-      $this->getMock('Drupal\Core\Config\Context\ContextInterface'),
       $plugin_manager,
       $plugin_manager,
       $plugin_manager,
@@ -104,10 +105,12 @@ protected function getSettingsForm(array $configs, array $definitions, array $co
     );
 
     if (!empty($config_names)) {
-      $plugin = $this->getMock('Drupal\Core\Plugin\PluginConfigFormInterface');
+      $plugin = $this->getMockBuilder('Drupal\aggregator\Plugin\AggregatorPluginSettingsBase')
+        ->disableOriginalConstructor()
+        ->getMock();
       $plugin
         ->expects($this->exactly(3))
-        ->method('getConfigNames')
+        ->method('getEditableConfigNames')
         ->will($this->returnValue($config_names));
       $plugin_manager
         ->expects($this->exactly(3))
diff --git a/core/modules/search/src/SearchPageListBuilder.php b/core/modules/search/src/SearchPageListBuilder.php
index f59c1cb..7b1c121 100644
--- a/core/modules/search/src/SearchPageListBuilder.php
+++ b/core/modules/search/src/SearchPageListBuilder.php
@@ -13,6 +13,7 @@
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Form\ConfigFormInterface;
+use Drupal\Core\Form\FormInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Url;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -22,7 +23,7 @@
  *
  * @see \Drupal\search\Entity\SearchPage
  */
-class SearchPageListBuilder extends DraggableListBuilder implements ConfigFormInterface {
+class SearchPageListBuilder extends DraggableListBuilder implements FormInterface, ConfigFormInterface {
 
   /**
    * The entities being listed.
diff --git a/core/modules/system/src/Form/ImageToolkitForm.php b/core/modules/system/src/Form/ImageToolkitForm.php
index ec9f8bd..f1b68bd 100644
--- a/core/modules/system/src/Form/ImageToolkitForm.php
+++ b/core/modules/system/src/Form/ImageToolkitForm.php
@@ -9,8 +9,8 @@
 
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Form\ConfigFormBase;
+use Drupal\Core\Form\ConfigFormInterface;
 use Drupal\Core\Form\FormStateInterface;
-use Drupal\Core\Form\PluginConfigFormInterface;
 use Drupal\Core\ImageToolkit\ImageToolkitManager;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -66,7 +66,7 @@ public function getEditableConfigNames() {
     $config_names = ['system.image'];
 
     foreach ($this->availableToolkits as $toolkit) {
-      if ($toolkit instanceof PluginConfigFormInterface) {
+      if ($toolkit instanceof ConfigFormInterface) {
         $config_names = array_merge($config_names, $toolkit->getEditableConfigNames());
       }
     }