diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTestBase.php b/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTestBase.php
index 61eee7e..1495f07 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTestBase.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigSchemaTestBase.php
@@ -2,12 +2,14 @@
 
 /**
  * @file
- * Contains Drupal\config\Tests\DefaultConfigTest.
+ * Contains Drupal\config\Tests\ConfigSchemaTestBase.
  */
 
 namespace Drupal\config\Tests;
 
+use Drupal\Core\Config\Schema\Mapping;
 use Drupal\Core\Config\Schema\Property;
+use Drupal\Core\Config\Schema\Sequence;
 use Drupal\Core\Config\TypedConfigManagerInterface;
 use Drupal\Core\TypedData\Type\BooleanInterface;
 use Drupal\Core\TypedData\Type\StringInterface;
@@ -38,6 +40,8 @@
   protected $configName;
 
   /**
+   * Global state for whether the config passed for a name.
+   *
    * @var boolean
    */
   protected $configPass;
@@ -110,17 +114,13 @@ protected function checkValue($key, $value) {
           if ($type == 'string' && ($element instanceof StringInterface || $element instanceof Property)) {
             $success = TRUE;
           }
-          // Null values are allowed for all types.
+          // Null values are allowed for all scalar types.
           if ($value === NULL) {
             $success = TRUE;
           }
         }
-        else {
-          // @todo throw an exception due to an incomplete schema. Only possible
-          //   once https://drupal.org/node/1910624 is complete.
-        }
-        $class = get_class($element);
         if (!$success) {
+          $class = get_class($element);
           $this->fail("{$this->configName}:$key has the wrong schema. Variable type is $type and schema class is $class.");
         }
       }
@@ -129,7 +129,18 @@ protected function checkValue($key, $value) {
       }
     }
     else {
-      // Any non-scalar value must be an array.
+      try {
+        $element = $this->schema->get($key);
+        if (!($element instanceof Mapping) && !($element instanceof Sequence)) {
+          $this->fail("{$this->configName}:$key is not defined as a mapping or sequence but is not a scalar value.");
+        }
+      }
+      catch (SchemaIncompleteException $e) {
+        $this->fail("{$this->configName}:$key has no schema.");
+      }
+
+      // Go on processing so we can get errors on all levels. Any non-scalar
+      // value must be an array so cast to an array.
       if (!is_array($value)) {
         $value = (array) $value;
       }