diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index f23a864..1598e50 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -459,7 +459,7 @@ function _theme($hook, $variables = array()) {
       // Only log a message when not trying theme suggestions ($hook being an
       // array).
       if (!isset($candidate)) {
-        \Drupal::logger('theme')->warning('Theme hook %hook not found.', array('%hook' => $hook));
+        trigger_error(sprintf("Theme hook %s not found.", $hook), E_USER_ERROR);
       }
       // There is no theme implementation for the hook passed. Return FALSE so
       // the function calling _theme() can differentiate between a hook that
diff --git a/core/modules/system/tests/modules/entity_test/src/EntityTestViewBuilder.php b/core/modules/system/tests/modules/entity_test/src/EntityTestViewBuilder.php
index 535faff..3456512 100644
--- a/core/modules/system/tests/modules/entity_test/src/EntityTestViewBuilder.php
+++ b/core/modules/system/tests/modules/entity_test/src/EntityTestViewBuilder.php
@@ -8,6 +8,7 @@
 namespace Drupal\entity_test;
 
 use Drupal\Component\Utility\String;
+use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityViewBuilder;
 
 /**
@@ -20,6 +21,15 @@ class EntityTestViewBuilder extends EntityViewBuilder {
   /**
    * {@inheritdoc}
    */
+  protected function getBuildDefaults(EntityInterface $entity, $view_mode, $langcode) {
+    $build = parent::getBuildDefaults($entity, $view_mode, $langcode);
+    unset($build['#theme']);
+    return $build;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function buildComponents(array &$build, array $entities, array $displays, $view_mode, $langcode = NULL) {
     parent::buildComponents($build, $entities, $displays, $view_mode, $langcode);