diff --git a/core/modules/language/src/Tests/Migrate/d6/MigrateDefaultLanguageTest.php b/core/modules/language/src/Tests/Migrate/d6/MigrateDefaultLanguageTest.php
index be60ac2..ff5965a 100644
--- a/core/modules/language/src/Tests/Migrate/d6/MigrateDefaultLanguageTest.php
+++ b/core/modules/language/src/Tests/Migrate/d6/MigrateDefaultLanguageTest.php
@@ -7,10 +7,11 @@
 
 namespace Drupal\language\Tests\Migrate\d6;
 
-use Drupal\migrate_drupal\Tests\d6\MigrateDrupal6TestBase;
+use Drupal\language\Entity\ConfigurableLanguage;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
 
 /**
- * Tests language default variable migration.
+ * Tests the default language variable migration.
  *
  * @group migrate_drupal_6
  */
@@ -22,22 +23,40 @@ class MigrateDefaultLanguageTest extends MigrateDrupal6TestBase {
   public static $modules = ['language'];
 
   /**
-   * Tests migration of the language_default variable to the
-   * system.site.default_langcode config key.
+   * Tests the migration of the language_default variable to the
+   * system.site.default_langcode config key, with an existing language.
    */
-  public function testMigration() {
-    // The default language of the test fixture is English. Change it to French
-    // before migrating, to be sure that the source site default language is
-    // migrated.
-    $value = 'O:8:"stdClass":11:{s:8:"language";s:2:"fr";s:4:"name";s:6:"French";s:6:"native";s:6:"French";s:9:"direction";s:1:"0";s:7:"enabled";i:1;s:7:"plurals";s:1:"0";s:7:"formula";s:0:"";s:6:"domain";s:0:"";s:6:"prefix";s:0:"";s:6:"weight";s:1:"0";s:10:"javascript";s:0:"";}';
+  public function testMigrationWithExistingLanguage() {
+    $this->doTestMigration('fr');
+  }
+
+  /**
+   * Tests the migration of the language_default variable to the
+   * system.site.default_langcode config key, with a non-existent language.
+   */
+  public function testMigrationWithNonExistentLanguage() {
+    $this->doTestMigration('tv');
+  }
+
+  /**
+   * Helper method to test the migration.
+   */
+  protected function doTestMigration($langcode) {
+    // The default language of the test fixture is English. Change it to
+    // something else before migrating, to be sure that the source site
+    // default language is migrated.
+    $value = 'O:8:"stdClass":11:{s:8:"language";s:2:"' . $langcode . '";s:4:"name";s:6:"French";s:6:"native";s:6:"French";s:9:"direction";s:1:"0";s:7:"enabled";i:1;s:7:"plurals";s:1:"0";s:7:"formula";s:0:"";s:6:"domain";s:0:"";s:6:"prefix";s:0:"";s:6:"weight";s:1:"0";s:10:"javascript";s:0:"";}';
     $this->sourceDatabase->update('variable')
       ->fields(array(
         'value' => $value
       ))
       ->condition('name', 'language_default' )
       ->execute();
+    $this->executeMigration('language');
     $this->executeMigration('d6_default_language');
-    $this->assertIdentical('fr', $this->config('system.site')->get('default_langcode'));
+    $default_language = ConfigurableLanguage::load($langcode);
+    $this->assertNotNull($default_language);
+    $this->assertIdentical($langcode, $this->config('system.site')->get('default_langcode'));
   }
 
 }