diff --git a/core/lib/Drupal/Core/Config/TypedConfigManager.php b/core/lib/Drupal/Core/Config/TypedConfigManager.php
index f587c6e..6fba132 100644
--- a/core/lib/Drupal/Core/Config/TypedConfigManager.php
+++ b/core/lib/Drupal/Core/Config/TypedConfigManager.php
@@ -152,9 +152,8 @@ public function getDefinition($base_plugin_id) {
       $type = $name;
     }
     else {
-      // If we don't have definition, return the 'default' element.
-      // This should map to 'undefined' type by default, unless overridden.
-      $type = 'default';
+      // If we don't have definition, return the 'undefined' element.
+      $type = 'undefined';
     }
     $definition = $definitions[$type];
     // Check whether this type is an extension of another one and compile it.
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTest.php
index 8b129bc..b372128 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTest.php
@@ -40,11 +40,11 @@ public function setUp() {
    * Tests the basic metadata retrieval layer.
    */
   function testSchemaMapping() {
-    // Nonexistent configuration key will have Unknown as metadata.
+    // Nonexistent configuration key will have Undefined as metadata.
     $this->assertIdentical(FALSE, \Drupal::service('config.typed')->hasConfigSchema('config_schema_test.no_such_key'));
     $definition = \Drupal::service('config.typed')->getDefinition('config_schema_test.no_such_key');
     $expected = array();
-    $expected['label'] = 'Unknown';
+    $expected['label'] = 'Undefined';
     $expected['class'] = '\Drupal\Core\Config\Schema\Undefined';
     $this->assertEqual($definition, $expected, 'Retrieved the right metadata for nonexistent configuration.');