diff --git a/core/authorize.php b/core/authorize.php
index 8a76fe4..3507f7f 100644
--- a/core/authorize.php
+++ b/core/authorize.php
@@ -23,7 +23,7 @@
 // Change the directory to the Drupal root.
 chdir('..');
 
-require_once __DIR__ . '/vendor/autoload.php';
+require_once __DIR__ . '/autoload.php';
 
 /**
  * Global flag to identify update.php and authorize.php runs.
diff --git a/core/autoload.php b/core/autoload.php
new file mode 100644
index 0000000..79b7fd3
--- /dev/null
+++ b/core/autoload.php
@@ -0,0 +1,15 @@
+<?php
+
+/**
+ * @file
+ * Drupal-specific autoload.php to be used instead of the one generated by
+ * Composer.
+ * Having a Drupal-specific autoload.php makes it easier to use a ClassLoader
+ * implementation different from the one provided by Composer.
+ */
+
+use Drupal\Core\Autoload\DrupalAutoloaderInit;
+
+require_once __DIR__ . '/lib/Drupal/Core/Autoload/DrupalAutoloaderInit.php';
+
+return DrupalAutoloaderInit::getLoader();
diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index e8350cf..5728a3c 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2719,7 +2719,7 @@ function arg($index = NULL, $path = NULL) {
  *   loader class when calling drupal_classloader() from settings.php. It is
  *   ignored otherwise.
  *
- * @return \Composer\Autoload\ClassLoader
+ * @return \Drupal\Core\Autoload\ClassLoader
  *   A ClassLoader class instance (or extension thereof).
  */
 function drupal_classloader($class_loader = NULL) {
@@ -2731,7 +2731,7 @@ function drupal_classloader($class_loader = NULL) {
   if (!isset($loader)) {
 
     // Retrieve the Composer ClassLoader for loading classes.
-    $loader = include __DIR__ . '/../vendor/autoload.php';
+    $loader = include __DIR__ . '/../autoload.php';
 
     // Register the class loader.
     // When configured to use APC, the ApcClassLoader is registered instead.
@@ -2761,7 +2761,10 @@ function drupal_classloader($class_loader = NULL) {
  */
 function drupal_classloader_register($name, $path) {
   $loader = drupal_classloader();
-  $loader->add('Drupal\\' . $name, DRUPAL_ROOT . '/' . $path . '/lib');
+  $loader->addPsr4('Drupal\\' . $name . '\\', array(
+    DRUPAL_ROOT . '/' . $path . '/lib/Drupal/' . $name,
+    DRUPAL_ROOT . '/' . $path . '/lib',
+  ));
 }
 
 /**
diff --git a/core/install.php b/core/install.php
index 7152fd8..e2900a2 100644
--- a/core/install.php
+++ b/core/install.php
@@ -8,7 +8,7 @@
 // Change the directory to the Drupal root.
 chdir('..');
 
-require_once __DIR__ . '/vendor/autoload.php';
+require_once __DIR__ . '/autoload.php';
 
 /**
  * Global flag to indicate the site is in installation mode.
diff --git a/core/lib/Drupal/Component/Plugin/Discovery/AnnotatedClassDiscovery.php b/core/lib/Drupal/Component/Plugin/Discovery/AnnotatedClassDiscovery.php
index 6110bd1..5264f5e 100644
--- a/core/lib/Drupal/Component/Plugin/Discovery/AnnotatedClassDiscovery.php
+++ b/core/lib/Drupal/Component/Plugin/Discovery/AnnotatedClassDiscovery.php
@@ -52,7 +52,7 @@ function __construct($plugin_namespaces = array(), $plugin_definition_annotation
   }
 
   /**
-   * Implements Drupal\Component\Plugin\Discovery\DiscoveryInterface::getDefinition().
+   * {@inheritdoc}
    */
   public function getDefinition($plugin_id) {
     $plugins = $this->getDefinitions();
@@ -60,7 +60,7 @@ public function getDefinition($plugin_id) {
   }
 
   /**
-   * Implements Drupal\Component\Plugin\Discovery\DiscoveryInterface::getDefinitions().
+   * {@inheritdoc}
    */
   public function getDefinitions() {
     $definitions = array();
@@ -77,7 +77,6 @@ public function getDefinitions() {
     // Search for classes within all PSR-0 namespace locations.
     foreach ($this->getPluginNamespaces() as $namespace => $dirs) {
       foreach ($dirs as $dir) {
-        $dir .= DIRECTORY_SEPARATOR . str_replace('\\', DIRECTORY_SEPARATOR, $namespace);
         if (file_exists($dir)) {
           foreach (new DirectoryIterator($dir) as $fileinfo) {
             // @todo Once core requires 5.3.6, use $fileinfo->getExtension().
diff --git a/core/lib/Drupal/Core/Autoload/ClassLoader.php b/core/lib/Drupal/Core/Autoload/ClassLoader.php
new file mode 100644
index 0000000..ef78b58
--- /dev/null
+++ b/core/lib/Drupal/Core/Autoload/ClassLoader.php
@@ -0,0 +1,377 @@
+<?php
+
+/**
+ * @file
+ * Contains Drupal\Core\Autoload\ClassLoader.
+ */
+
+namespace Drupal\Core\Autoload;
+
+/**
+ * ClassLoader implements a PSR-0 class loader
+ *
+ * See https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-0.md
+ *
+ *     $loader = new \Composer\Autoload\ClassLoader();
+ *
+ *     // register classes with namespaces
+ *     $loader->add('Symfony\Component', __DIR__.'/component');
+ *     $loader->add('Symfony',           __DIR__.'/framework');
+ *
+ *     // activate the autoloader
+ *     $loader->register();
+ *
+ *     // to enable searching the include path (eg. for PEAR packages)
+ *     $loader->setUseIncludePath(true);
+ *
+ * In this example, if you try to use a class in the Symfony\Component
+ * namespace or one of its children (Symfony\Component\Console for instance),
+ * the autoloader will first look for the class under the component/
+ * directory, and it will then fallback to the framework/ directory if not
+ * found before giving up.
+ *
+ * This class is loosely based on the Symfony UniversalClassLoader.
+ *
+ * @author Fabien Potencier <fabien@symfony.com>
+ * @author Jordi Boggiano <j.boggiano@seld.be>
+ */
+class ClassLoader {
+
+  // PSR-4
+  private $prefixLengthsPsr4 = array();
+  private $prefixDirsPsr4 = array();
+  private $fallbackDirsPsr4 = array();
+
+  // PSR-0
+  private $prefixesPsr0 = array();
+  private $fallbackDirsPsr0 = array();
+
+  private $useIncludePath = false;
+  private $classMap = array();
+
+  const PREDICTOR_INDEX = 9;
+
+  public function getPrefixes() {
+    return call_user_func_array('array_merge', $this->prefixesPsr0);
+  }
+
+  public function getPrefixesPsr4() {
+    return $this->prefixDirsPsr4;
+  }
+
+  public function getFallbackDirs() {
+    return $this->fallbackDirsPsr0;
+  }
+
+  public function getFallbackDirsPsr4() {
+    return $this->fallbackDirsPsr4;
+  }
+
+  public function getClassMap() {
+    return $this->classMap;
+  }
+
+  /**
+   * @param array $classMap Class to filename map
+   */
+  public function addClassMap(array $classMap) {
+    if ($this->classMap) {
+      $this->classMap = array_merge($this->classMap, $classMap);
+    }
+    else {
+      $this->classMap = $classMap;
+    }
+  }
+
+  /**
+   * Registers a set of PSR-0 directories for a given prefix, either
+   * appending or prepending to the ones previously set for this prefix.
+   *
+   * @param string       $prefix  The prefix
+   * @param array|string $paths   The PSR-0 root directories
+   * @param bool         $prepend Whether to prepend the directories
+   */
+  public function add($prefix, $paths, $prepend = false) {
+    if (!$prefix) {
+      if ($prepend) {
+        $this->fallbackDirsPsr0 = array_merge(
+          (array) $paths,
+          $this->fallbackDirsPsr0
+        );
+      }
+      else {
+        $this->fallbackDirsPsr0 = array_merge(
+          $this->fallbackDirsPsr0,
+          (array) $paths
+        );
+      }
+
+      return;
+    }
+
+    $first = $prefix[0];
+    if (!isset($this->prefixesPsr0[$first][$prefix])) {
+      $this->prefixesPsr0[$first][$prefix] = (array) $paths;
+
+      return;
+    }
+    if ($prepend) {
+      $this->prefixesPsr0[$first][$prefix] = array_merge(
+        (array) $paths,
+        $this->prefixesPsr0[$first][$prefix]
+      );
+    }
+    else {
+      $this->prefixesPsr0[$first][$prefix] = array_merge(
+        $this->prefixesPsr0[$first][$prefix],
+        (array) $paths
+      );
+    }
+  }
+
+  /**
+   * Registers a set of PSR-4 directories for a given namespace, either
+   * appending or prepending to the ones previously set for this namespace.
+   *
+   * @param string $prefix  The prefix/namespace, with trailing '\\'
+   * @param array|string $paths   The PSR-0 base directories
+   * @param bool $prepend Whether to prepend the directories
+   * @throws \Exception
+   */
+  public function addPsr4($prefix, $paths, $prepend = false) {
+    if (!$prefix) {
+      // Register directories for the root namespace.
+      if ($prepend) {
+        $this->fallbackDirsPsr4 = array_merge(
+          (array) $paths,
+          $this->fallbackDirsPsr4
+        );
+      }
+      else {
+        $this->fallbackDirsPsr4 = array_merge(
+          $this->fallbackDirsPsr4,
+          (array) $paths
+        );
+      }
+    }
+    elseif (!isset($this->prefixDirsPsr4[$prefix])) {
+      // Register directories for a new namespace.
+      $length = strlen($prefix);
+      if ('\\' !== $prefix[$length - 1]) {
+        throw new \Exception("A non-empty PSR-4 prefix must end with a namespace separator.");
+      }
+      if ($length > self::PREDICTOR_INDEX) {
+        $predictor = $prefix[0] . $prefix[self::PREDICTOR_INDEX];
+        $this->prefixLengthsPsr4[$predictor][$prefix] = $length;
+      }
+      else {
+        $this->prefixLengthsPsr4[$prefix[0]][$prefix] = $length;
+      }
+      $this->prefixDirsPsr4[$prefix] = (array) $paths;
+    }
+    elseif ($prepend) {
+      // Prepend directories for an already registered namespace.
+      $this->prefixDirsPsr4[$prefix] = array_merge(
+        (array) $paths,
+        $this->prefixDirsPsr4[$prefix]
+      );
+    }
+    else {
+      // Append directories for an already registered namespace.
+      $this->prefixDirsPsr4[$prefix] = array_merge(
+        $this->prefixDirsPsr4[$prefix],
+        (array) $paths
+      );
+    }
+  }
+
+  /**
+   * Registers a set of PSR-0 directories for a given prefix,
+   * replacing any others previously set for this prefix.
+   *
+   * @param string       $prefix The prefix
+   * @param array|string $paths  The PSR-0 base directories
+   */
+  public function set($prefix, $paths) {
+    if (!$prefix) {
+      $this->fallbackDirsPsr0 = (array) $paths;
+    }
+    else {
+      $this->prefixesPsr0[$prefix[0]][$prefix] = (array) $paths;
+    }
+  }
+
+  /**
+   * Registers a set of PSR-4 directories for a given namespace,
+   * replacing any others previously set for this namespace.
+   *
+   * @param string $prefix  The prefix/namespace, with trailing '\\'
+   * @param array|string $paths   The PSR-4 base directories
+   * @throws \Exception
+   */
+  public function setPsr4($prefix, $paths) {
+    if (!$prefix) {
+      $this->fallbackDirsPsr4 = (array) $paths;
+    }
+    else {
+      $length = strlen($prefix);
+      if ('\\' !== $prefix[$length - 1]) {
+        throw new \Exception("A non-empty PSR-4 prefix must end with a namespace separator.");
+      }
+      if ($length > self::PREDICTOR_INDEX) {
+        $predictor = $prefix[0] . $prefix[self::PREDICTOR_INDEX];
+        $this->prefixLengthsPsr4[$predictor][$prefix] = $length;
+      }
+      else {
+        $this->prefixLengthsPsr4[$prefix[0]][$prefix] = $length;
+      }
+      $this->prefixDirsPsr4[$prefix] = (array) $paths;
+    }
+  }
+
+  /**
+   * Turns on searching the include path for class files.
+   *
+   * @param bool $useIncludePath
+   */
+  public function setUseIncludePath($useIncludePath) {
+    $this->useIncludePath = $useIncludePath;
+  }
+
+  /**
+   * Can be used to check if the autoloader uses the include path to check
+   * for classes.
+   *
+   * @return bool
+   */
+  public function getUseIncludePath() {
+    return $this->useIncludePath;
+  }
+
+  /**
+   * Registers this instance as an autoloader.
+   *
+   * @param bool $prepend Whether to prepend the autoloader or not
+   */
+  public function register($prepend = false) {
+    spl_autoload_register(array($this, 'loadClass'), true, $prepend);
+  }
+
+  /**
+   * Unregisters this instance as an autoloader.
+   */
+  public function unregister() {
+    spl_autoload_unregister(array($this, 'loadClass'));
+  }
+
+  /**
+   * Loads the given class or interface.
+   *
+   * @param  string    $class The name of the class
+   * @return bool|null True if loaded, null otherwise
+   */
+  public function loadClass($class) {
+    if ($file = $this->findFile($class)) {
+      include $file;
+
+      return true;
+    }
+  }
+
+  /**
+   * Finds the path to the file where the class is defined.
+   *
+   * @param string $class The name of the class
+   *
+   * @return string|false The path if found, false otherwise
+   */
+  public function findFile($class) {
+    // work around for PHP 5.3.0 - 5.3.2 https://bugs.php.net/50731
+    if ('\\' == $class[0]) {
+      $class = substr($class, 1);
+    }
+
+    // class map lookup
+    if (isset($this->classMap[$class])) {
+      return $this->classMap[$class];
+    }
+
+    // PSR-4 lookup
+    $logicalPathPsr4 = strtr($class, '\\', DIRECTORY_SEPARATOR) . '.php';
+
+    $first = $class[0];
+    if (isset($class[self::PREDICTOR_INDEX])) {
+      $predictor = $first . $class[self::PREDICTOR_INDEX];
+      if (isset($this->prefixLengthsPsr4[$predictor])) {
+        foreach ($this->prefixLengthsPsr4[$predictor] as $prefix => $length) {
+          if (0 === strpos($class, $prefix)) {
+            foreach ($this->prefixDirsPsr4[$prefix] as $dir) {
+              if (file_exists($file = $dir . DIRECTORY_SEPARATOR . substr($logicalPathPsr4, $length))) {
+                return $file;
+              }
+            }
+          }
+        }
+      }
+    }
+
+    if (isset($this->prefixLengthsPsr4[$first])) {
+      foreach ($this->prefixLengthsPsr4[$first] as $prefix => $length) {
+        if (0 === strpos($class, $prefix)) {
+          foreach ($this->prefixDirsPsr4[$prefix] as $dir) {
+            if (file_exists($file = $dir . DIRECTORY_SEPARATOR . substr($logicalPathPsr4, $length))) {
+              return $file;
+            }
+          }
+        }
+      }
+    }
+
+    // PSR-4 fallback dirs
+    foreach ($this->fallbackDirsPsr4 as $dir) {
+      if (file_exists($file = $dir . DIRECTORY_SEPARATOR . $logicalPathPsr4)) {
+        return $file;
+      }
+    }
+
+    // PSR-0 lookup
+    if (false !== $pos = strrpos($class, '\\')) {
+      // namespaced class name
+      $logicalPathPsr0
+        = substr($logicalPathPsr4, 0, $pos + 1)
+        . strtr(substr($logicalPathPsr4, $pos + 1), '_', DIRECTORY_SEPARATOR)
+      ;
+    }
+    else {
+      // PEAR-like class name
+      $logicalPathPsr0 = strtr($class, '_', DIRECTORY_SEPARATOR) . '.php';
+    }
+
+    if (isset($this->prefixesPsr0[$first])) {
+      foreach ($this->prefixesPsr0[$first] as $prefix => $dirs) {
+        if (0 === strpos($class, $prefix)) {
+          foreach ($dirs as $dir) {
+            if (file_exists($file = $dir . DIRECTORY_SEPARATOR . $logicalPathPsr0)) {
+              return $file;
+            }
+          }
+        }
+      }
+    }
+
+    // PSR-0 fallback dirs
+    foreach ($this->fallbackDirsPsr0 as $dir) {
+      if (file_exists($file = $dir . DIRECTORY_SEPARATOR . $logicalPathPsr0)) {
+        return $file;
+      }
+    }
+
+    // PSR-0 include paths.
+    if ($this->useIncludePath && $file = stream_resolve_include_path($logicalPathPsr0)) {
+      return $file;
+    }
+
+    // Remember that this class does not exist.
+    return $this->classMap[$class] = false;
+  }
+}
diff --git a/core/lib/Drupal/Core/Autoload/DrupalAutoloaderInit.php b/core/lib/Drupal/Core/Autoload/DrupalAutoloaderInit.php
new file mode 100644
index 0000000..87f6478
--- /dev/null
+++ b/core/lib/Drupal/Core/Autoload/DrupalAutoloaderInit.php
@@ -0,0 +1,65 @@
+<?php
+
+/**
+ * @file
+ * Contains Drupal\Core\Autoload\DrupalAutoloaderInit.
+ */
+
+namespace Drupal\Core\Autoload;
+
+class DrupalAutoloaderInit
+{
+  private static $loader;
+
+  public static function loadClassLoader($class) {
+    if ('Drupal\Core\Autoload\ClassLoader' === $class) {
+      require __DIR__ . '/ClassLoader.php';
+    }
+  }
+
+  public static function getLoader() {
+    if (null !== self::$loader) {
+      return self::$loader;
+    }
+
+    spl_autoload_register(array('Drupal\Core\Autoload\DrupalAutoloaderInit', 'loadClassLoader'), true, true);
+    self::$loader = $loader = new ClassLoader();
+    spl_autoload_unregister(array('Drupal\Core\Autoload\DrupalAutoloaderInit', 'loadClassLoader'));
+
+    $coreDir = dirname(dirname(dirname(dirname(__DIR__))));
+    $vendorDir = $coreDir . '/vendor';
+    $composerDir = $vendorDir . '/composer';
+    $baseDir = dirname($coreDir);
+
+    $includePaths = require $composerDir . '/include_paths.php';
+    array_push($includePaths, get_include_path());
+    set_include_path(join(PATH_SEPARATOR, $includePaths));
+
+    $map = require $composerDir . '/autoload_namespaces.php';
+    // Register core namespaces as PSR-4 instead of PSR-0,
+    // to let the autoloader handle them with priority.
+    // @todo Do this via composer.json, once Composer supports PSR-4.
+    unset($map['Drupal\Core']);
+    unset($map['Drupal\Component']);
+    unset($map['Drupal\Driver']);
+    $loader->setPsr4('Drupal\Core\\', $baseDir . '/core/lib/Drupal/Core');
+    $loader->setPsr4('Drupal\Component\\', $baseDir . '/core/lib/Drupal/Component');
+    $loader->setPsr4('Drupal\Driver\\', $baseDir . '/core/lib/Drupal/Driver');
+    foreach ($map as $namespace => $path) {
+      $loader->set($namespace, $path);
+    }
+
+    $classMap = require $composerDir . '/autoload_classmap.php';
+    if ($classMap) {
+      $loader->addClassMap($classMap);
+    }
+
+    $loader->register(true);
+
+    // @todo This can be updated once Composer provides a autoload_files.php.
+    require $vendorDir . '/kriswallsmith/assetic/src/functions.php';
+    require $baseDir . '/core/lib/Drupal.php';
+
+    return $loader;
+  }
+}
diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index 1bf9c05..23ea4db 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -19,7 +19,7 @@
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpKernel\HttpKernelInterface;
 use Symfony\Component\HttpKernel\TerminableInterface;
-use Composer\Autoload\ClassLoader;
+use Drupal\Core\Autoload\ClassLoader;
 
 /**
  * The DrupalKernel class is the core of Drupal itself.
@@ -97,7 +97,7 @@ class DrupalKernel implements DrupalKernelInterface, TerminableInterface {
   /**
    * The classloader object.
    *
-   * @var \Composer\Autoload\ClassLoader
+   * @var \Drupal\Core\Autoload\ClassLoader
    */
   protected $classLoader;
 
@@ -150,7 +150,7 @@ class DrupalKernel implements DrupalKernelInterface, TerminableInterface {
    *   String indicating the environment, e.g. 'prod' or 'dev'. Used by
    *   Symfony\Component\HttpKernel\Kernel::__construct(). Drupal does not use
    *   this value currently. Pass 'prod'.
-   * @param \Composer\Autoload\ClassLoader $class_loader
+   * @param \Drupal\Core\Autoload\ClassLoader $class_loader
    *   (optional) The classloader is only used if $storage is not given or
    *   the load from storage fails and a container rebuild is required. In
    *   this case, the loaded modules will be registered with this loader in
@@ -218,7 +218,7 @@ public function discoverServiceProviders() {
       $this->moduleList = isset($module_list['enabled']) ? $module_list['enabled'] : array();
     }
     $module_filenames = $this->getModuleFileNames();
-    $this->registerNamespaces($this->getModuleNamespaces($module_filenames));
+    $this->registerNamespacesPsr4($this->getModuleNamespacesPsr4($module_filenames));
 
     // Load each module's serviceProvider class.
     foreach ($this->moduleList as $module => $weight) {
@@ -402,8 +402,8 @@ protected function initializeContainer() {
       // All namespaces must be registered before we attempt to use any service
       // from the container.
       $container_modules = $this->container->getParameter('container.modules');
-      $namespaces_before = $this->classLoader->getPrefixes();
-      $this->registerNamespaces($this->getModuleNamespaces($container_modules));
+      $namespaces_before = $this->classLoader->getPrefixesPsr4();
+      $this->registerNamespacesPsr4($this->getModuleNamespacesPsr4($container_modules));
 
       // If 'container.modules' is wrong, the container must be rebuilt.
       if (!isset($this->moduleList)) {
@@ -416,9 +416,9 @@ protected function initializeContainer() {
         // registerNamespaces() performs a merge rather than replace, so to
         // effectively remove erroneous registrations, we must replace them with
         // empty arrays.
-        $namespaces_after = $this->classLoader->getPrefixes();
+        $namespaces_after = $this->classLoader->getPrefixesPsr4();
         $namespaces_before += array_fill_keys(array_diff(array_keys($namespaces_after), array_keys($namespaces_before)), array());
-        $this->registerNamespaces($namespaces_before);
+        $this->registerNamespacesPsr4($namespaces_before);
       }
     }
 
@@ -492,14 +492,15 @@ protected function buildContainer() {
     $container->setParameter('container.modules', $this->getModuleFileNames());
 
     // Get a list of namespaces and put it onto the container.
-    $namespaces = $this->getModuleNamespaces($this->getModuleFileNames());
+    $namespaces = $this->getModuleNamespacesPsr4($this->getModuleFileNames());
     // Add all components in \Drupal\Core and \Drupal\Component that have a
     // Plugin directory.
     foreach (array('Core', 'Component') as $parent_directory) {
       $path = DRUPAL_ROOT . '/core/lib/Drupal/' . $parent_directory;
+      $parent_namespace = 'Drupal\\' . $parent_directory;
       foreach (new \DirectoryIterator($path) as $component) {
         if (!$component->isDot() && is_dir($component->getPathname() . '/Plugin')) {
-          $namespaces['Drupal\\' . $parent_directory  .'\\' . $component->getFilename()] = DRUPAL_ROOT . '/core/lib';
+          $namespaces[$parent_namespace . '\\' . $component->getFilename()] = $path . '/' . $component->getFilename();
         }
       }
     }
@@ -632,7 +633,28 @@ protected function getModuleFileNames() {
   }
 
   /**
-   * Gets the namespaces of each enabled module.
+   * Gets the namespaces of each enabled module,
+   * each with their PSR-4 directories.
+   *
+   * @param array $moduleFileNames
+   * @return array
+   */
+  protected function getModuleNamespacesPsr4($moduleFileNames) {
+    $namespaces = array();
+    foreach ($moduleFileNames as $module => $filename) {
+      // @todo Remove lib/Drupal/$module, once the switch to PSR-4 is complete.
+      $namespaces["Drupal\\$module"][] = DRUPAL_ROOT . '/' . dirname($filename) . '/lib/Drupal/' . $module;
+      $namespaces["Drupal\\$module"][] = DRUPAL_ROOT . '/' . dirname($filename) . '/lib';
+    }
+    return $namespaces;
+  }
+
+  /**
+   * Gets the namespaces of each enabled module,
+   * each with its PSR-0 directory.
+   *
+   * @param array $moduleFileNames
+   * @return array
    */
   protected function getModuleNamespaces($moduleFileNames) {
     $namespaces = array();
@@ -643,7 +665,20 @@ protected function getModuleNamespaces($moduleFileNames) {
   }
 
   /**
-   * Registers a list of namespaces.
+   * Registers a list of namespaces with PSR-4 directories.
+   *
+   * @param array $namespaces
+   */
+  protected function registerNamespacesPsr4(array $namespaces = array()) {
+    foreach ($namespaces as $prefix => $paths) {
+      $this->classLoader->addPsr4($prefix . '\\', $paths);
+    }
+  }
+
+  /**
+   * Registers a list of namespaces with PSR-0 directories.
+   *
+   * @param array $namespaces
    */
   protected function registerNamespaces(array $namespaces = array()) {
     foreach ($namespaces as $prefix => $path) {
diff --git a/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
index e033caf..ae208af 100644
--- a/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
@@ -15,17 +15,23 @@
 class AnnotatedClassDiscovery extends ComponentAnnotatedClassDiscovery {
 
   /**
-   * The subdirectory within a namespace to look for plugins.
+   * A suffix to append to each PSR-4 directory associated with a base
+   * namespace, to form the directories where plugins are found.
    *
-   * If the plugins are in the top level of the namespace and not within a
-   * subdirectory, set this to an empty string.
+   * @var string
+   */
+  protected $directorySuffix = '';
+
+  /**
+   * A suffix to append to each base namespace, to obtain the namespaces where
+   * plugins are found.
    *
    * @var string
    */
-  protected $subdir = '';
+  protected $namespaceSuffix = '';
 
   /**
-   * An object containing the namespaces to look for plugin implementations.
+   * A list of base namespaces with their PSR-4 directories.
    *
    * @var \Traversable
    */
@@ -47,7 +53,11 @@ class AnnotatedClassDiscovery extends ComponentAnnotatedClassDiscovery {
    */
   function __construct($subdir, \Traversable $root_namespaces, $plugin_definition_annotation_name = 'Drupal\Component\Annotation\Plugin') {
     if ($subdir) {
-      $this->subdir = str_replace('/', '\\', $subdir);
+      if ('/' !== $subdir[0]) {
+        $subdir = '/' . $subdir;
+      }
+      $this->directorySuffix = $subdir;
+      $this->namespaceSuffix = str_replace('/', '\\', $subdir);
     }
     $this->rootNamespacesIterator = $root_namespaces;
     $plugin_namespaces = array();
@@ -92,11 +102,18 @@ protected function getProviderFromNamespace($namespace) {
    */
   protected function getPluginNamespaces() {
     $plugin_namespaces = array();
-    foreach ($this->rootNamespacesIterator as $namespace => $dir) {
-      if ($this->subdir) {
-        $namespace .= "\\{$this->subdir}";
+    if ($this->namespaceSuffix) {
+      foreach ($this->rootNamespacesIterator as $namespace => $dirs) {
+        $namespace .= $this->namespaceSuffix;
+        foreach ((array) $dirs as $dir) {
+          $plugin_namespaces[$namespace][] = $dir . $this->directorySuffix;
+        }
+      }
+    }
+    else {
+      foreach ($this->rootNamespacesIterator as $namespace => $dirs) {
+        $plugin_namespaces[$namespace] = (array) $dirs;
       }
-      $plugin_namespaces[$namespace] = array($dir);
     }
 
     return $plugin_namespaces;
diff --git a/core/modules/block/tests/lib/Drupal/block/Tests/BlockBaseTest.php b/core/modules/block/tests/Drupal/block/Tests/BlockBaseTest.php
similarity index 100%
rename from core/modules/block/tests/lib/Drupal/block/Tests/BlockBaseTest.php
rename to core/modules/block/tests/Drupal/block/Tests/BlockBaseTest.php
diff --git a/core/modules/block/tests/lib/Drupal/block/Tests/BlockFormControllerTest.php b/core/modules/block/tests/Drupal/block/Tests/BlockFormControllerTest.php
similarity index 100%
rename from core/modules/block/tests/lib/Drupal/block/Tests/BlockFormControllerTest.php
rename to core/modules/block/tests/Drupal/block/Tests/BlockFormControllerTest.php
diff --git a/core/modules/block/tests/lib/Drupal/block/Tests/Plugin/views/display/BlockTest.php b/core/modules/block/tests/Drupal/block/Tests/Plugin/views/display/BlockTest.php
similarity index 100%
rename from core/modules/block/tests/lib/Drupal/block/Tests/Plugin/views/display/BlockTest.php
rename to core/modules/block/tests/Drupal/block/Tests/Plugin/views/display/BlockTest.php
diff --git a/core/modules/comment/comment.install b/core/modules/comment/comment.install
index 04e1291..0ff09b1 100644
--- a/core/modules/comment/comment.install
+++ b/core/modules/comment/comment.install
@@ -13,7 +13,11 @@ function comment_uninstall() {
   variable_del('comment_block_count');
   $node_types = array_keys(node_type_get_types());
   Drupal::entityManager()->addNamespaces(new ArrayIterator(array(
-    'Drupal\comment' => DRUPAL_ROOT . '/core/modules/comment/lib',
+    'Drupal\comment' => array(
+      DRUPAL_ROOT . '/core/modules/comment/lib/Drupal/comment',
+      DRUPAL_ROOT . '/core/modules/comment/lib',
+      DRUPAL_ROOT . '/core/modules/comment/src',
+    ),
   )));
   drupal_classloader_register('comment', 'core/modules/comment');
   foreach ($node_types as $node_type) {
diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index 8d441f4..b98d528 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -454,21 +454,28 @@ function simpletest_test_get_all() {
       $all_data = $module_data + system_rebuild_theme_data();
       $all_data += drupal_system_listing('/\.profile$/', 'profiles', 'name');
       foreach ($all_data as $name => $data) {
-        // Build directory in which the test files would reside.
-        $tests_dir = DRUPAL_ROOT . '/' . dirname($data->uri) . '/lib/Drupal/' . $name . '/Tests';
+        $extension_dir = DRUPAL_ROOT . '/' . dirname($data->uri);
+
+        // Build directories in which the test files would reside.
+        $tests_dirs = array(
+          $extension_dir . '/lib/Drupal/' . $name . '/Tests',
+          $extension_dir . '/lib/Tests',
+          $extension_dir . '/tests/Drupal/' . $name . '/Tests',
+          $extension_dir . '/tests/lib',
+        );
+
+        $namespace = 'Drupal\\' . $name . '\Tests\\';
+
         // Scan it for test files if it exists.
-        if (is_dir($tests_dir)) {
-          $files = file_scan_directory($tests_dir, '/.*\.php/');
-          if (!empty($files)) {
-            $basedir = DRUPAL_ROOT . '/' . dirname($data->uri) . '/lib/';
-            foreach ($files as $file) {
-              // Convert the file name into the namespaced class name.
-              $replacements = array(
-                '/' => '\\',
-                $basedir => '',
-                '.php' => '',
-              );
-              $classes[] = strtr($file->uri, $replacements);
+        foreach ($tests_dirs as $tests_dir) {
+          if (is_dir($tests_dir)) {
+            $files = file_scan_directory($tests_dir, '/.*\.php/');
+            if (!empty($files)) {
+              $strlen = strlen($tests_dir) + 1;
+              // Convert the file names into the namespaced class names.
+              foreach ($files as $file) {
+                $classes[] = $namespace . str_replace('/', '\\', substr($file->uri, $strlen, -4));
+              }
             }
           }
         }
@@ -526,8 +533,14 @@ function simpletest_classloader_register() {
   foreach ($types as $type => $info) {
     $matches = drupal_system_listing('/^' . DRUPAL_PHP_FUNCTION_PATTERN . '\.' . $info['extension'] . '$/', $info['dir']);
     foreach ($matches as $name => $file) {
+      // @todo Register PSR-4 namespace directories, once our classloader supports it.
+      // See https://drupal.org/node/2058867
       drupal_classloader_register($name, dirname($file->uri));
-      $classloader->add('Drupal\\' . $name . '\\Tests', DRUPAL_ROOT . '/' . dirname($file->uri) . '/tests');
+      $extension_dir = dirname($file->uri);
+      $classloader->addPsr4('Drupal\\' . $name . '\\Tests\\', array(
+        $extension_dir . '/tests/Drupal/' . $name . '/Tests',
+        $extension_dir . '/tests/lib',
+      ));
       // While being there, prime drupal_get_filename().
       drupal_get_filename($type, $name, $file->uri);
     }
diff --git a/core/modules/statistics/statistics.php b/core/modules/statistics/statistics.php
index ed132e8..22acde2 100644
--- a/core/modules/statistics/statistics.php
+++ b/core/modules/statistics/statistics.php
@@ -9,7 +9,7 @@
 chdir('../../..');
 
 // Load the Drupal bootstrap.
-require_once dirname(dirname(__DIR__)) . '/vendor/autoload.php';
+require_once dirname(dirname(__DIR__)) . '/autoload.php';
 require_once dirname(dirname(__DIR__)) . '/includes/bootstrap.inc';
 drupal_bootstrap(DRUPAL_BOOTSTRAP_VARIABLES);
 
diff --git a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/AnnotatedClassDiscoveryTest.php b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/AnnotatedClassDiscoveryTest.php
index d2fba9b..52bd303 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/AnnotatedClassDiscoveryTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/AnnotatedClassDiscoveryTest.php
@@ -57,7 +57,13 @@ public function setUp() {
         'provider' => 'plugin_test',
       ),
     );
-    $namespaces = new \ArrayObject(array('Drupal\plugin_test' => DRUPAL_ROOT . '/core/modules/system/tests/modules/plugin_test/lib'));
+    $namespaces = new \ArrayObject(array(
+      'Drupal\plugin_test' => array(
+        // @todo Remove lib/Drupal/$module, once the switch to PSR-4 is complete.
+        DRUPAL_ROOT . '/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test',
+        DRUPAL_ROOT . '/core/modules/system/tests/modules/plugin_test/lib',
+      ),
+    ));
     $this->discovery = new AnnotatedClassDiscovery('Plugin/plugin_test/fruit', $namespaces);
     $this->emptyDiscovery = new AnnotatedClassDiscovery('Plugin/non_existing_module/non_existing_plugin_type', $namespaces);
   }
diff --git a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/CustomAnnotationClassDiscoveryTest.php b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/CustomAnnotationClassDiscoveryTest.php
index d61c013..17bbfa5 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/CustomAnnotationClassDiscoveryTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/CustomAnnotationClassDiscoveryTest.php
@@ -41,7 +41,13 @@ protected function setUp() {
         'provider' => 'plugin_test',
       ),
     );
-    $root_namespaces = new \ArrayObject(array('Drupal\plugin_test' => DRUPAL_ROOT . '/core/modules/system/tests/modules/plugin_test/lib'));
+    $root_namespaces = new \ArrayObject(array(
+      'Drupal\plugin_test' => array(
+        // @todo Remove lib/Drupal/$module, once the switch to PSR-4 is complete.
+        DRUPAL_ROOT . '/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test',
+        DRUPAL_ROOT . '/core/modules/system/tests/modules/plugin_test/lib',
+      ),
+    ));
 
     $this->discovery = new AnnotatedClassDiscovery('Plugin/plugin_test/custom_annotation', $root_namespaces, 'Drupal\plugin_test\Plugin\Annotation\PluginExample');
     $this->emptyDiscovery = new AnnotatedClassDiscovery('Plugin/non_existing_module/non_existing_plugin_type', $root_namespaces, 'Drupal\plugin_test\Plugin\Annotation\PluginExample');
diff --git a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php
index c005300..b817c68 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Plugin/Discovery/CustomDirectoryAnnotatedClassDiscoveryTest.php
@@ -39,7 +39,13 @@ protected function setUp() {
         'provider' => 'plugin_test',
       ),
     );
-    $namespaces = new \ArrayObject(array('Drupal\plugin_test' => DRUPAL_ROOT . '/core/modules/system/tests/modules/plugin_test/lib'));
+    $namespaces = new \ArrayObject(array(
+      'Drupal\plugin_test' => array(
+        // @todo Remove lib/Drupal/$module, once the switch to PSR-4 is complete.
+        DRUPAL_ROOT . '/core/modules/system/tests/modules/plugin_test/lib/Drupal/plugin_test',
+        DRUPAL_ROOT . '/core/modules/system/tests/modules/plugin_test/lib',
+      ),
+    ));
     $this->discovery = new AnnotatedClassDiscovery('', $namespaces);
     $empty_namespaces = new \ArrayObject();
     $this->emptyDiscovery = new AnnotatedClassDiscovery('', $empty_namespaces);
diff --git a/core/modules/system/tests/http.php b/core/modules/system/tests/http.php
index 662031f..10f4e20 100644
--- a/core/modules/system/tests/http.php
+++ b/core/modules/system/tests/http.php
@@ -18,6 +18,6 @@
 
 // Change current directory to the Drupal root.
 chdir('../../../..');
-require_once dirname(dirname(dirname(__DIR__))) . '/vendor/autoload.php';
+require_once dirname(dirname(dirname(__DIR__))) . '/autoload.php';
 require_once dirname(dirname(dirname(__DIR__))) . '/includes/bootstrap.inc';
 drupal_handle_request(TRUE);
diff --git a/core/modules/system/tests/https.php b/core/modules/system/tests/https.php
index 247e6e5..54c8afa 100644
--- a/core/modules/system/tests/https.php
+++ b/core/modules/system/tests/https.php
@@ -20,6 +20,6 @@
 
 // Change current directory to the Drupal root.
 chdir('../../../..');
-require_once dirname(dirname(dirname(__DIR__))) . '/vendor/autoload.php';
+require_once dirname(dirname(dirname(__DIR__))) . '/autoload.php';
 require_once dirname(dirname(dirname(__DIR__))) . '/includes/bootstrap.inc';
 drupal_handle_request(TRUE);
diff --git a/core/modules/taxonomy/taxonomy.install b/core/modules/taxonomy/taxonomy.install
index 7648ba0..a4494e2 100644
--- a/core/modules/taxonomy/taxonomy.install
+++ b/core/modules/taxonomy/taxonomy.install
@@ -14,7 +14,11 @@
  */
 function taxonomy_uninstall() {
   Drupal::entityManager()->addNamespaces(new ArrayIterator(array(
-    'Drupal\taxonomy' => DRUPAL_ROOT . '/core/modules/taxonomy/lib',
+    'Drupal\taxonomy' => array(
+      // @todo Remove lib/Drupal/$module, once the switch to PSR-4 is complete.
+      DRUPAL_ROOT . '/core/modules/taxonomy/lib/Drupal/taxonomy',
+      DRUPAL_ROOT . '/core/modules/taxonomy/lib',
+    ),
   )));
   drupal_classloader_register('taxonomy', 'core/modules/taxonomy');
   // Remove taxonomy_term bundles.
diff --git a/core/modules/views/lib/Drupal/views/Plugin/Discovery/ViewsHandlerDiscovery.php b/core/modules/views/lib/Drupal/views/Plugin/Discovery/ViewsHandlerDiscovery.php
index a3a08c0..09f5255 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/Discovery/ViewsHandlerDiscovery.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/Discovery/ViewsHandlerDiscovery.php
@@ -22,13 +22,6 @@ class ViewsHandlerDiscovery extends AnnotatedClassDiscovery {
   protected $type;
 
   /**
-   * An object containing the namespaces to look for plugin implementations.
-   *
-   * @var \Traversable
-   */
-  protected $rootNamespacesIterator;
-
-  /**
    * Constructs a ViewsHandlerDiscovery object.
    *
    * @param string $type
@@ -39,15 +32,7 @@ class ViewsHandlerDiscovery extends AnnotatedClassDiscovery {
    */
   function __construct($type, \Traversable $root_namespaces) {
     $this->type = $type;
-    $this->rootNamespacesIterator = $root_namespaces;
-
-    $plugin_namespaces = array();
-    foreach ($root_namespaces as $namespace => $dir) {
-      $plugin_namespaces["$namespace\\Plugin\\views\\{$type}"] = array($dir);
-    }
-
-    $this->pluginNamespaces = $plugin_namespaces;
-    $this->pluginDefinitionAnnotationName = 'Drupal\Component\Annotation\PluginID';
+    parent::__construct("Plugin/views/$type", $root_namespaces, 'Drupal\Component\Annotation\PluginID');
   }
 
   /**
@@ -62,16 +47,4 @@ public function getDefinitions() {
     return $definitions;
   }
 
-  /**
-   * {@inheritdoc}
-   */
-  protected function getPluginNamespaces() {
-    $plugin_namespaces = array();
-    foreach ($this->rootNamespacesIterator as $namespace => $dir) {
-      $plugin_namespaces["$namespace\\Plugin\\views\\{$this->type}"] = array($dir);
-    }
-
-    return $plugin_namespaces;
-  }
-
 }
diff --git a/core/scripts/run-tests.sh b/core/scripts/run-tests.sh
index 31ea371..d274252 100755
--- a/core/scripts/run-tests.sh
+++ b/core/scripts/run-tests.sh
@@ -4,7 +4,7 @@
  * This script runs Drupal tests from command line.
  */
 
-require_once __DIR__ . '/../vendor/autoload.php';
+require_once __DIR__ . '/../autoload.php';
 
 use Drupal\Core\StreamWrapper\PublicStream;
 
diff --git a/core/scripts/switch-psr4.sh b/core/scripts/switch-psr4.sh
new file mode 100644
index 0000000..ed76b47
--- /dev/null
+++ b/core/scripts/switch-psr4.sh
@@ -0,0 +1,122 @@
+#!/bin/php
+<?php
+
+/**
+ * @file
+ * Moves class files in extensions to their PSR-4 location.
+ */
+
+// Determine DRUPAL_ROOT.
+$dir = dirname(__FILE__);
+while (!defined('DRUPAL_ROOT')) {
+  if (is_dir($dir . '/core')) {
+    define('DRUPAL_ROOT', $dir);
+  }
+  $dir = dirname($dir);
+}
+
+process_extensions_base_dir(DRUPAL_ROOT . '/core/modules');
+process_extensions_base_dir(DRUPAL_ROOT . '/core/profiles');
+
+function process_extensions_base_dir($dir) {
+  /**
+   * @var SplFileInfo $fileinfo
+   */
+  foreach (new \DirectoryIterator($dir) as $fileinfo) {
+    if ($fileinfo->isDot()) {
+      // do nothing
+    }
+    elseif ($fileinfo->isDir()) {
+      process_candidate_dir($fileinfo->getPathname());
+    }
+  }
+}
+
+function process_candidate_dir($dir) {
+  foreach (new \DirectoryIterator($dir) as $fileinfo) {
+    if ($fileinfo->isDot()) {
+      // Ignore "." and "..".
+    }
+    elseif ($fileinfo->isDir()) {
+      // It's a directory.
+      switch ($fileinfo->getFilename()) {
+        case 'lib':
+        case 'module_autoload_test':
+          // Ignore these directory names.
+          continue;
+        default:
+          // Look for more extensions in subdirectories.
+          process_candidate_dir($fileinfo->getPathname());
+      }
+    }
+    else {
+      // It's a file.
+      if (preg_match('/^(.+).info.yml$/', $fileinfo->getFilename(), $m)) {
+        // It's a *.info.yml file, so we found an extension directory.
+        $extension_name = $m[1];
+      }
+    }
+  }
+  if (isset($extension_name)) {
+    process_extension($extension_name, $dir);
+  }
+}
+
+function process_extension($name, $dir) {
+
+  // Move main module class files.
+  if (is_dir("$dir/lib/Drupal/$name")) {
+    // This is a module directory with a PSR-0 /lib/ folder.
+    // Move to src/ as a temporary location.
+    if (!rename($src = "$dir/lib/Drupal/$name", $dest = "$dir/src")) {
+      throw new Exception("Rename $src to $dest failed.");
+    }
+  }
+
+  // Move class files in tests directory.
+  if (is_dir("$dir/tests/Drupal/$name/Tests")) {
+    // Move to tests/src/ as a temporary location.
+    if (!rename($src = "$dir/tests/Drupal/$name/Tests", $dest = "$dir/tests/src")) {
+      throw new Exception("Rename $src to $dest failed.");
+    }
+  }
+
+  // Clean up empty directories.
+  foreach (array(
+    "lib/Drupal/$name",
+    'lib/Drupal',
+    'lib',
+    "tests/Drupal/$name/Tests",
+    "tests/Drupal/$name",
+    "tests/Drupal",
+  ) as $subdir) {
+    if (!is_dir("$dir/$subdir")) {
+      continue;
+    }
+    if (!is_dir_empty("$dir/$subdir")) {
+      throw new Exception("$dir/$subdir is not empty.");
+    }
+    rmdir("$dir/$subdir");
+  }
+
+  // Move back to lib/ or tests/lib/.
+  if (is_dir("$dir/src")) {
+    rename("$dir/src", "$dir/lib");
+  }
+  if (is_dir("$dir/tests/src")) {
+    rename("$dir/tests/src", "$dir/tests/lib");
+  }
+}
+
+function is_dir_empty($dir) {
+  if (!is_readable($dir)) {
+    return NULL;
+  }
+  $handle = opendir($dir);
+  while (false !== ($entry = readdir($handle))) {
+    if ($entry != "." && $entry != "..") {
+      return FALSE;
+    }
+  }
+  return TRUE;
+}
diff --git a/core/tests/bootstrap.php b/core/tests/bootstrap.php
index 66c4be4..e0be3f8 100644
--- a/core/tests/bootstrap.php
+++ b/core/tests/bootstrap.php
@@ -1,7 +1,7 @@
 <?php
 
 // Register the namespaces we'll need to autoload from.
-$loader = require __DIR__ . "/../vendor/autoload.php";
+$loader = require __DIR__ . "/../autoload.php";
 $loader->add('Drupal\\Tests', __DIR__);
 
 foreach (scandir(__DIR__ . "/../modules") as $module) {
diff --git a/core/update.php b/core/update.php
index ac36b2a..0238871 100644
--- a/core/update.php
+++ b/core/update.php
@@ -22,7 +22,7 @@
 // Change the directory to the Drupal root.
 chdir('..');
 
-require_once __DIR__ . '/vendor/autoload.php';
+require_once __DIR__ . '/autoload.php';
 
 // Exit early if an incompatible PHP version would cause fatal errors.
 // The minimum version is specified explicitly, as DRUPAL_MINIMUM_PHP is not
diff --git a/index.php b/index.php
index 426aa22..5f5ada6 100644
--- a/index.php
+++ b/index.php
@@ -8,7 +8,7 @@
  * See COPYRIGHT.txt and LICENSE.txt files in the "core" directory.
  */
 
-require_once __DIR__ . '/core/vendor/autoload.php';
+require_once __DIR__ . '/core/autoload.php';
 require_once __DIR__ . '/core/includes/bootstrap.inc';
 
 try {