diff --git a/core/lib/Drupal/Core/Config/StorableConfigBase.php b/core/lib/Drupal/Core/Config/StorableConfigBase.php
index b5289ef..5eab003 100644
--- a/core/lib/Drupal/Core/Config/StorableConfigBase.php
+++ b/core/lib/Drupal/Core/Config/StorableConfigBase.php
@@ -179,9 +179,7 @@ protected function castValue($key, $value) {
     $element = $this->getSchemaWrapper()->get($key);
     // Do not cast value if it is unknown or defined to be ignored.
     if ($element && ($element instanceof Undefined)) {
-      if ($element['type'] == 'undefined') {
-        throw new ConfigException(String::format("The configuration property @key is undefined.", array('@key' => $element->getFullName())));
-      }
+      throw new ConfigException(String::format("The configuration property @key is undefined.", array('@key' => $element->getFullName())));
     }
     elseif ($element && ($element instanceof Ignore)) {
       // Do validate the value (may throw UnsupportedDataTypeConfigException)