diff -u b/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
--- b/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -132,13 +132,13 @@
       $cache_file = $class . '.php';
 
       // First, try to load.
-      if (!class_exists($class)) {
+      if (!class_exists($class, FALSE)) {
         $this->storage->load($cache_file);
       }
       // If the load succeeded or the class already existed, use it.
-      if (class_exists($class)) {
-        $fully_qualified_classname = '\\' . $class;
-        $this->container = new $fully_qualified_classname;
+      if (class_exists($class, FALSE)) {
+        $fully_qualified_class_name = '\\' . $class;
+        $this->container = new $fully_qualified_class_name;
       }
     }
     if (!isset($this->container)) {