diff --git a/core/core.services.yml b/core/core.services.yml
index 9139f90..c90e862 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -980,6 +980,7 @@ services:
     class: Drupal\Core\EventSubscriber\ConfigImportSubscriber
     tags:
       - { name: event_subscriber }
+    arguments: ['@theme_handler']
   config_snapshot_subscriber:
     class: Drupal\Core\EventSubscriber\ConfigSnapshotSubscriber
     tags:
diff --git a/core/lib/Drupal/Core/Config/ConfigImporter.php b/core/lib/Drupal/Core/Config/ConfigImporter.php
index 4f28425..9a4ebcd 100644
--- a/core/lib/Drupal/Core/Config/ConfigImporter.php
+++ b/core/lib/Drupal/Core/Config/ConfigImporter.php
@@ -240,11 +240,12 @@ public function getStorageComparer() {
    */
   public function reset() {
     $this->storageComparer->reset();
+    // Empty all the lists.
     foreach ($this->storageComparer->getAllCollectionNames() as $collection) {
       $this->processedConfiguration[$collection] = $this->storageComparer->getEmptyChangelist();
     }
-    $this->processedExtensions = $this->getEmptyExtensionsProcessedList();
-    $this->createExtensionChangelist();
+    $this->extensionChangelist = $this->processedExtensions = $this->getEmptyExtensionsProcessedList();
+
     $this->validated = FALSE;
     $this->processedSystemTheme = FALSE;
     return $this;
@@ -359,6 +360,9 @@ protected function setProcessedExtension($type, $op, $name) {
    * Populates the extension change list.
    */
   protected function createExtensionChangelist() {
+    // Create an empty changelist.
+    $this->extensionChangelist = $this->getEmptyExtensionsProcessedList();
+
     // Read the extensions information to determine changes.
     $current_extensions = $this->storageComparer->getTargetStorage()->read('core.extension');
     $new_extensions = $this->storageComparer->getSourceStorage()->read('core.extension');
@@ -396,7 +400,7 @@ protected function createExtensionChangelist() {
     //  0 1 actions
     // @todo Move this sorting functionality to the extension system.
     array_multisort(array_values($module_list), SORT_ASC, array_keys($module_list), SORT_DESC, $module_list);
-    $uninstall = array_intersect(array_keys($module_list), $uninstall);
+    $this->extensionChangelist['module']['uninstall'] = array_intersect(array_keys($module_list), $uninstall);
 
     // Determine which modules to install.
     $install = array_keys(array_diff_key($new_extensions['module'], $current_extensions['module']));
@@ -404,22 +408,19 @@ protected function createExtensionChangelist() {
     // (with dependencies installed first, and modules of the same weight sorted
     // in alphabetical order).
     $module_list = array_reverse($module_list);
-    $install = array_intersect(array_keys($module_list), $install);
+    $this->extensionChangelist['module']['install'] = array_intersect(array_keys($module_list), $install);
+    if ($missing_modules = array_diff($install, $this->extensionChangelist['module']['install'])) {
+      $this->logError($this->formatPlural(
+        count($missing_modules),
+        'Unable to install module %modules since it does not exist.',
+        'Unable to install modules %modules since they do not exist.',
+        array('%modules' => implode(', ',$missing_modules))
+      ));
+    }
 
     // Work out what themes to install and to uninstall.
-    $theme_install = array_keys(array_diff_key($new_extensions['theme'], $current_extensions['theme']));
-    $theme_uninstall = array_keys(array_diff_key($current_extensions['theme'], $new_extensions['theme']));
-
-    $this->extensionChangelist = array(
-      'module' => array(
-        'uninstall' => $uninstall,
-        'install' => $install,
-      ),
-      'theme' => array(
-        'install' => $theme_install,
-        'uninstall' => $theme_uninstall,
-      ),
-    );
+    $this->extensionChangelist['theme']['install'] = array_keys(array_diff_key($new_extensions['theme'], $current_extensions['theme']));
+    $this->extensionChangelist['theme']['uninstall'] = array_keys(array_diff_key($current_extensions['theme'], $new_extensions['theme']));
   }
 
   /**
@@ -434,7 +435,7 @@ protected function createExtensionChangelist() {
    * @return array
    *   An array of extension names.
    */
-  protected function getExtensionChangelist($type, $op = NULL) {
+  public function getExtensionChangelist($type, $op = NULL) {
     if ($op) {
       return $this->extensionChangelist[$type][$op];
     }
diff --git a/core/lib/Drupal/Core/EventSubscriber/ConfigImportSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/ConfigImportSubscriber.php
index f17d5bd..d3023cc 100644
--- a/core/lib/Drupal/Core/EventSubscriber/ConfigImportSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/ConfigImportSubscriber.php
@@ -8,9 +8,11 @@
 namespace Drupal\Core\EventSubscriber;
 
 use Drupal\Core\Config\Config;
+use Drupal\Core\Config\ConfigImporter;
 use Drupal\Core\Config\ConfigImporterEvent;
 use Drupal\Core\Config\ConfigImportValidateEventSubscriberBase;
 use Drupal\Core\Config\ConfigNameException;
+use Drupal\Core\Extension\ThemeHandlerInterface;
 
 /**
  * Config import subscriber for config import events.
@@ -18,6 +20,23 @@
 class ConfigImportSubscriber extends ConfigImportValidateEventSubscriberBase {
 
   /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface
+   */
+  protected $themeHandler;
+
+  /**
+   * Constructs the ConfigImportSubscriber.
+   *
+   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
+   *   The theme handler.
+   */
+  public function __construct(ThemeHandlerInterface $theme_handler) {
+    $this->themeHandler = $theme_handler;
+  }
+
+  /**
    * Validates the configuration to be imported.
    *
    * @param \Drupal\Core\Config\ConfigImporterEvent $event
@@ -37,6 +56,122 @@ public function onConfigImporterValidate(ConfigImporterEvent $event) {
         }
       }
     }
+    $config_importer = $event->getConfigImporter();
+    if ($config_importer->getStorageComparer()->getSourceStorage()->exists('core.extension')) {
+      $this->validateModules($config_importer);
+      $this->validateThemes($config_importer);
+      $this->validateDependencies($config_importer);
+    }
+    else {
+      $config_importer->logError($this->t('The core.extension configuration does not exist.'));
+    }
+  }
+
+  /**
+   * Validates module installations and uninstallations.
+   *
+   * @param \Drupal\Core\Config\ConfigImporter $config_importer
+   *   The configuration importer.
+   */
+  protected function validateModules(ConfigImporter $config_importer) {
+    $core_extension = $config_importer->getStorageComparer()->getSourceStorage()->read('core.extension');
+    // Get a list of modules with dependency weights as values.
+    $module_data = system_rebuild_module_data();
+    $nonexistent_modules = array_keys(array_diff_key($core_extension['module'], $module_data));
+    foreach ($nonexistent_modules as $module) {
+      $config_importer->logError($this->t('Unable to install module %module since it does not exist.', array('%module' => $module)));
+    }
+
+    // Ensure that module dependencies are respected.
+    $uninstalls = $config_importer->getExtensionChangelist('module', 'uninstall');
+    foreach ($uninstalls as $module) {
+      foreach (array_keys($module_data[$module]->required_by) as $dependent_module) {
+        if ($module_data[$dependent_module]->status && !in_array($dependent_module, $uninstalls, TRUE)) {
+          $module_name = $module_data[$module]->info['name'];
+          $dependent_module_name = $module_data[$dependent_module]->info['name'];
+          $config_importer->logError($this->t('Unable to uninstall module %module since %dependent_module is installed.', array('%module' => $module_name, '%dependent_module' => $dependent_module_name)));
+        }
+      }
+    }
+  }
+
+  /**
+   * Validates theme installations and uninstallations.
+   *
+   * @param \Drupal\Core\Config\ConfigImporter $config_importer
+   *   The configuration importer.
+   */
+  protected function validateThemes(ConfigImporter $config_importer) {
+    // Get all themes including those that are not installed.
+    $theme_data = $this->themeHandler->rebuildThemeData();
+    foreach ($config_importer->getExtensionChangelist('theme', 'install') as $theme) {
+      if (!isset($theme_data[$theme])) {
+        $config_importer->logError($this->t('Unable to install theme %theme since it does not exist.', array('%theme' => $theme)));
+      }
+    }
+
+    $uninstalls = $config_importer->getExtensionChangelist('theme', 'uninstall');
+    foreach ($uninstalls as $theme) {
+      foreach (array_keys($theme_data[$theme]->required_by) as $dependent_theme) {
+        if ($theme_data[$dependent_theme]->status && !in_array($dependent_theme, $uninstalls, TRUE)) {
+          $theme_name = $theme_data[$theme]->info['name'];
+          $dependent_theme_name = $theme_data[$dependent_theme]->info['name'];
+          $config_importer->logError($this->t('Unable to uninstall theme %theme since %dependent_theme is installed.', array('%theme' => $theme_name, '%dependent_theme' => $dependent_theme_name)));
+        }
+      }
+    }
+  }
+
+  /**
+   * Validates configuration being imported does not have unmet dependencies.
+   *
+   * @param \Drupal\Core\Config\ConfigImporter $config_importer
+   *   The configuration importer.
+   */
+  protected function validateDependencies(ConfigImporter $config_importer) {
+    $core_extension = $config_importer->getStorageComparer()->getSourceStorage()->read('core.extension');
+    $existing_dependencies = [
+      'config' => $config_importer->getStorageComparer()->getSourceStorage()->listAll(),
+      'module' => array_keys($core_extension['module']),
+      'theme' => array_keys($core_extension['theme']),
+    ];
+
+    // Validate the dependencies of all the configuration. We have to validate
+    // the entire tree because existing configuration might depend on
+    // configuration that is being deleted.
+    foreach ($config_importer->getStorageComparer()->getSourceStorage()->listAll() as $name) {
+      // Ensure that the config owner is installed. This checks all
+      // configuration including configuration entities.
+      list($owner,) = explode('.', $name, 2);
+      if ($owner !== 'core' && !isset($core_extension['module'][$owner]) && !isset($core_extension['theme'][$owner])) {
+        $config_importer->logError($this->t('Configuration %name depends on the %owner extension that will not be installed after import.', array('%name' => $name, '%owner' => $owner)));
+        continue;
+      }
+
+      $data = $config_importer->getStorageComparer()->getSourceStorage()->read($name);
+      // Configuration entities can be identified by having a dependencies and a
+      // UUID key. Check the dependencies to ensure they are met.
+      if (isset($data['dependencies']) && isset($data['uuid'])) {
+        $dependencies_to_check = array_intersect_key($data['dependencies'], array_flip(['module', 'theme', 'config']));
+        foreach ($dependencies_to_check as $type => $dependencies) {
+          $diffs = array_diff($dependencies, $existing_dependencies[$type]);
+          if (!empty($diffs)) {
+            switch ($type) {
+              case 'module':
+                $config_importer->logError($this->t('Configuration %name depends on a module that will not be installed after import.', array('%name' => $name)));
+                break;
+              case 'theme':
+                $config_importer->logError($this->t('Configuration %name depends on a theme that will not be installed after import.', array('%name' => $name)));
+                break;
+              case 'config':
+                $config_importer->logError($this->t('Configuration %name depends on configuration that will not exist after import.', array('%name' => $name)));
+                break;
+            }
+          }
+        }
+      }
+    }
+
   }
 
 }
diff --git a/core/modules/config/src/Form/ConfigSync.php b/core/modules/config/src/Form/ConfigSync.php
index b97218b..ae21f01 100644
--- a/core/modules/config/src/Form/ConfigSync.php
+++ b/core/modules/config/src/Form/ConfigSync.php
@@ -340,7 +340,7 @@ public function submitForm(array &$form, FormStateInterface $form_state) {
       }
       catch (ConfigImporterException $e) {
         // There are validation errors.
-        drupal_set_message($this->t('The configuration synchronization failed validation.'));
+        drupal_set_message($this->t('The staged configuration cannot be imported because it failed validation for the following reasons:'), 'error');
         foreach ($config_importer->getErrors() as $message) {
           drupal_set_message($message, 'error');
         }
diff --git a/core/modules/config/src/Tests/ConfigImportUITest.php b/core/modules/config/src/Tests/ConfigImportUITest.php
index ba44925..0d3a088 100644
--- a/core/modules/config/src/Tests/ConfigImportUITest.php
+++ b/core/modules/config/src/Tests/ConfigImportUITest.php
@@ -326,7 +326,7 @@ public function testImportValidation() {
     $this->drupalPostForm(NULL, array(), t('Import all'));
 
     // Verify that the validation messages appear.
-    $this->assertText('The configuration synchronization failed validation.');
+    $this->assertText('The staged configuration cannot be imported because it failed validation for the following reasons:');
     $this->assertText('Config import validate error 1.');
     $this->assertText('Config import validate error 2.');
 
@@ -453,4 +453,35 @@ public function testEntityBundleDelete() {
     $this->assertNoText(format_string('core.entity_form_display.node.@type.default', array('@type' => $node_type->id())));
   }
 
+  /**
+   * Tests config importer cannot uninstall extensions which are depended on.
+   *
+   * @see \Drupal\Core\EventSubscriber\ConfigImportSubscriber
+   */
+  public function testExtensionValidation() {
+    \Drupal::service('module_installer')->install(['node']);
+    \Drupal::service('theme_handler')->install(['bartik']);
+    $this->rebuildContainer();
+
+    $staging = $this->container->get('config.storage.staging');
+    $this->copyConfig($this->container->get('config.storage'), $staging);
+    $core = $staging->read('core.extension');
+    // Node depends on text.
+    unset($core['module']['text']);
+    // Bartik depends on classy.
+    unset($core['theme']['classy']);
+    // This module does not exist.
+    $core['module']['does_not_exist'] = 0;
+    // This theme does not exist.
+    $core['theme']['does_not_exist'] = 0;
+    $staging->write('core.extension', $core);
+
+    $this->drupalPostForm('admin/config/development/configuration', array(), t('Import all'));
+    $this->assertText('The staged configuration cannot be imported because it failed validation for the following reasons:');
+    $this->assertText('Unable to uninstall module Text since Node is installed.');
+    $this->assertText('Unable to uninstall theme Classy since Bartik is installed.');
+    $this->assertText('Unable to install module does_not_exist since it does not exist.');
+    $this->assertText('Unable to install theme does_not_exist since it does not exist.');
+  }
+
 }
diff --git a/core/modules/config/src/Tests/ConfigImporterTest.php b/core/modules/config/src/Tests/ConfigImporterTest.php
index ebd6378..f1c16a6 100644
--- a/core/modules/config/src/Tests/ConfigImporterTest.php
+++ b/core/modules/config/src/Tests/ConfigImporterTest.php
@@ -105,7 +105,7 @@ function testSiteUuidValidate() {
     $staging->write('system.site', $config_data);
     try {
       $this->configImporter->reset()->import();
-      $this->assertFalse(FALSE, 'ConfigImporterException not thrown, invalid import was not stopped due to mis-matching site UUID.');
+      $this->fail('ConfigImporterException not thrown, invalid import was not stopped due to mis-matching site UUID.');
     }
     catch (ConfigImporterException $e) {
       $this->assertEqual($e->getMessage(), 'There were errors validating the config synchronization.');
@@ -541,4 +541,61 @@ function testIsInstallable() {
     $this->assertTrue($this->container->get('config.storage')->exists($config_name));
   }
 
+  /**
+   * Tests dependency validation during configuration import.
+   *
+   * @see \Drupal\Core\EventSubscriber\ConfigImportSubscriber
+   * @see \Drupal\Core\Config\ConfigImporter::createExtensionChangelist()
+   */
+  public function testUnmetDependency() {
+    $storage = $this->container->get('config.storage');
+    $staging = $this->container->get('config.storage.staging');
+
+    // Test an unknown configuration owner.
+    $staging->write('unknown.config', ['test' => 'test']);
+
+    // Make a config entity have unmet dependencies.
+    $config_entity_data = $staging->read('config_test.dynamic.dotted.default');
+    $config_entity_data['dependencies'] = ['module' => ['unknown']];
+    $staging->write('config_test.dynamic.dotted.module', $config_entity_data);
+    $config_entity_data['dependencies'] = ['theme' => ['unknown']];
+    $staging->write('config_test.dynamic.dotted.theme', $config_entity_data);
+    $config_entity_data['dependencies'] = ['config' => ['unknown']];
+    $staging->write('config_test.dynamic.dotted.config', $config_entity_data);
+
+    // Make an active config depend on something that is missing in staging.
+    // The whole configuration needs to be consistent not only the updated one.
+    $config_entity_data['dependencies'] = [];
+    $storage->write('config_test.dynamic.dotted.deleted', $config_entity_data);
+    $config_entity_data['dependencies'] = ['config' => ['config_test.dynamic.dotted.deleted']];
+    $storage->write('config_test.dynamic.dotted.existing', $config_entity_data);
+    $staging->write('config_test.dynamic.dotted.existing', $config_entity_data);
+
+    // Add a module and a theme that do not exist.
+    $extensions = $staging->read('core.extension');
+    $extensions['module']['unknown_module'] = 0;
+    $extensions['theme']['unknown_theme'] = 0;
+    $staging->write('core.extension', $extensions);
+    try {
+      $this->configImporter->reset()->import();
+      $this->fail('ConfigImporterException not thrown, invalid import was not stopped due to missing dependencies.');
+    }
+    catch (ConfigImporterException $e) {
+      $this->assertEqual($e->getMessage(), 'There were errors validating the config synchronization.');
+      $error_log = $this->configImporter->getErrors();
+      $expected = [
+        'Unable to install module <em class="placeholder">unknown_module</em> since it does not exist.',
+        'Unable to install theme <em class="placeholder">unknown_theme</em> since it does not exist.',
+        'Configuration <em class="placeholder">config_test.dynamic.dotted.config</em> depends on configuration that will not exist after import.',
+        'Configuration <em class="placeholder">config_test.dynamic.dotted.existing</em> depends on configuration that will not exist after import.',
+        'Configuration <em class="placeholder">config_test.dynamic.dotted.module</em> depends on a module that will not be installed after import.',
+        'Configuration <em class="placeholder">config_test.dynamic.dotted.theme</em> depends on a theme that will not be installed after import.',
+        'Configuration <em class="placeholder">unknown.config</em> depends on the <em class="placeholder">unknown</em> extension that will not be installed after import.'
+      ];
+      foreach ($expected as $expected_message) {
+        $this->assertTrue(in_array($expected_message, $error_log), $expected_message);
+      }
+    }
+  }
+
 }
diff --git a/core/modules/field/src/Tests/FieldImportDeleteUninstallUiTest.php b/core/modules/field/src/Tests/FieldImportDeleteUninstallUiTest.php
index 53998e7..de793dd 100644
--- a/core/modules/field/src/Tests/FieldImportDeleteUninstallUiTest.php
+++ b/core/modules/field/src/Tests/FieldImportDeleteUninstallUiTest.php
@@ -23,7 +23,7 @@ class FieldImportDeleteUninstallUiTest extends FieldTestBase {
    *
    * @var array
    */
-  public static $modules = array('entity_test', 'telephone', 'config', 'filter', 'text');
+  public static $modules = array('entity_test', 'telephone', 'config', 'filter', 'datetime');
 
   protected function setUp() {
     parent::setUp();
@@ -48,14 +48,14 @@ public function testImportDeleteUninstall() {
     ))->save();
 
     // Create a text field.
-    $text_field_storage = entity_create('field_storage_config', array(
-      'field_name' => 'field_text',
+    $date_field_storage = entity_create('field_storage_config', array(
+      'field_name' => 'field_date',
       'entity_type' => 'entity_test',
-      'type' => 'text',
+      'type' => 'datetime',
     ));
-    $text_field_storage->save();
+    $date_field_storage->save();
     entity_create('field_config', array(
-      'field_storage' => $text_field_storage,
+      'field_storage' => $date_field_storage,
       'bundle' => 'entity_test',
     ))->save();
 
@@ -63,14 +63,14 @@ public function testImportDeleteUninstall() {
     $entity = entity_create('entity_test');
     $value = '+0123456789';
     $entity->field_tel = $value;
-    $entity->field_text = $this->randomMachineName(20);
+    $entity->field_date = time();
     $entity->name->value = $this->randomMachineName();
     $entity->save();
 
     // Delete the text field before exporting configuration so that we can test
     // that deleted fields that are provided by modules that will be uninstalled
     // are also purged and that the UI message includes such fields.
-    $text_field_storage->delete();
+    $date_field_storage->delete();
 
     // Verify entity has been created properly.
     $id = $entity->id();
@@ -95,22 +95,13 @@ public function testImportDeleteUninstall() {
     // synchronization is correct.
     $this->assertText('This synchronization will delete data from the field entity_test.field_tel.');
 
-    // Stage an uninstall of the text module to test the message for multiple
-    // fields.
-    unset($core_extension['module']['text']);
+    // Stage an uninstall of the datetime module to test the message for
+    // multiple fields.
+    unset($core_extension['module']['datetime']);
     $staging->write('core.extension', $core_extension);
+
     $this->drupalGet('admin/config/development/configuration');
-    $this->assertText('This synchronization will delete data from the fields: entity_test.field_tel, entity_test.field_text.');
-    // Delete all the text fields in staging, entity_test_install() adds quite
-    // a few.
-    foreach (\Drupal::entityManager()->getFieldMap() as $entity_type => $fields) {
-      foreach ($fields as $field_name => $info) {
-        if ($info['type'] == 'text') {
-          $staging->delete("field.storage.$entity_type.$field_name");
-          $staging->delete("field.field.$entity_type.$entity_type.$field_name");
-        }
-      }
-    }
+    $this->assertText('This synchronization will delete data from the fields: entity_test.field_tel, entity_test.field_date.');
 
     // This will purge all the data, delete the field and uninstall the
     // Telephone and Text modules.
diff --git a/core/modules/system/src/SystemConfigSubscriber.php b/core/modules/system/src/SystemConfigSubscriber.php
index 765b824..204d685 100644
--- a/core/modules/system/src/SystemConfigSubscriber.php
+++ b/core/modules/system/src/SystemConfigSubscriber.php
@@ -7,32 +7,58 @@
 
 namespace Drupal\system;
 
+use Drupal\Core\Config\ConfigEvents;
 use Drupal\Core\Config\ConfigImporterEvent;
-use Drupal\Core\Config\ConfigImportValidateEventSubscriberBase;
-use Drupal\Core\Config\StorageDispatcher;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 
 /**
  * System Config subscriber.
  */
-class SystemConfigSubscriber extends ConfigImportValidateEventSubscriberBase {
+class SystemConfigSubscriber implements EventSubscriberInterface {
+  use StringTranslationTrait;
 
   /**
    * Checks that the configuration synchronization is valid.
    *
-   * This event listener implements two checks:
-   *   - prevents deleting all configuration.
-   *   - checks that the system.site:uuid's in the source and target match.
+   * This event listener prevents deleting all configuration. If there is
+   * nothing to import then event propagation is stopped because there is no
+   * config import to validate.
    *
-   * @param ConfigImporterEvent $event
+   * @param \Drupal\Core\Config\ConfigImporterEvent $event
    *   The config import event.
    */
-  public function onConfigImporterValidate(ConfigImporterEvent $event) {
+  public function onConfigImporterValidateNotEmpty(ConfigImporterEvent $event) {
     $importList = $event->getConfigImporter()->getStorageComparer()->getSourceStorage()->listAll();
     if (empty($importList)) {
       $event->getConfigImporter()->logError($this->t('This import is empty and if applied would delete all of your configuration, so has been rejected.'));
+      $event->stopPropagation();
     }
+  }
+
+  /**
+   * Checks that the configuration synchronization is valid.
+   *
+   * This event listener checks that the system.site:uuid's in the source and
+   * target match.
+   *
+   * @param ConfigImporterEvent $event
+   *   The config import event.
+   */
+  public function onConfigImporterValidateSiteUUID(ConfigImporterEvent $event) {
     if (!$event->getConfigImporter()->getStorageComparer()->validateSiteUuid()) {
       $event->getConfigImporter()->logError($this->t('Site UUID in source storage does not match the target storage.'));
     }
   }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    // The empty check has a high priority so that is can stop propagation if
+    // there is no configuration to import.
+    $events[ConfigEvents::IMPORT_VALIDATE][] = array('onConfigImporterValidateNotEmpty', 512);
+    $events[ConfigEvents::IMPORT_VALIDATE][] = array('onConfigImporterValidateSiteUUID', 256);
+    return $events;
+  }
 }