diff --git a/core/lib/Drupal/Core/Config/Schema/Ignore.php b/core/lib/Drupal/Core/Config/Schema/Ignore.php
index a616306..20701b8 100644
--- a/core/lib/Drupal/Core/Config/Schema/Ignore.php
+++ b/core/lib/Drupal/Core/Config/Schema/Ignore.php
@@ -11,4 +11,11 @@
  * Configuration property to ignore.
  */
 class Ignore extends Element {
+
+  /**
+   * {@inheritdoc}.
+   */
+  public function validate() {
+    return TRUE;
+  }
 }
diff --git a/core/lib/Drupal/Core/Config/Schema/Undefined.php b/core/lib/Drupal/Core/Config/Schema/Undefined.php
index 6e98a1a..1bcf744 100644
--- a/core/lib/Drupal/Core/Config/Schema/Undefined.php
+++ b/core/lib/Drupal/Core/Config/Schema/Undefined.php
@@ -11,4 +11,11 @@
  * Undefined configuration element.
  */
 class Undefined extends Element {
+
+  /**
+   * {@inheritdoc}.
+   */
+  public function validate() {
+    return isset($this->value);
+  }
 }