diff --git a/core/lib/Drupal/Core/Config/Schema/Mapping.php b/core/lib/Drupal/Core/Config/Schema/Mapping.php
index e63d2e3..28f22e8 100644
--- a/core/lib/Drupal/Core/Config/Schema/Mapping.php
+++ b/core/lib/Drupal/Core/Config/Schema/Mapping.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\Core\Config\Schema;
 
+use Drupal\Core\TypedData\ComplexDataInterface;
+
 /**
  * Defines a mapping configuration element.
  *
@@ -20,7 +22,7 @@
  * Read https://drupal.org/node/1905070 for more details about configuration
  * schema, types and type resolution.
  */
-class Mapping extends ArrayElement {
+class Mapping extends ArrayElement implements ComplexDataInterface {
 
   /**
    * {@inheritdoc}
diff --git a/core/lib/Drupal/Core/TypedData/ListDataDefinition.php b/core/lib/Drupal/Core/TypedData/ListDataDefinition.php
index f140e53..b710a75 100644
--- a/core/lib/Drupal/Core/TypedData/ListDataDefinition.php
+++ b/core/lib/Drupal/Core/TypedData/ListDataDefinition.php
@@ -101,13 +101,6 @@ public function getItemDefinition() {
   }
 
   /**
-   * {@inheritdoc}
-   */
-  public function getElementDefinition($name) {
-    return $this->getItemDefinition();
-  }
-
-  /**
    * Sets the item definition.
    *
    * @param \Drupal\Core\TypedData\DataDefinition $definition