diff -u b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
--- b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
+++ b/core/lib/Drupal/Core/Plugin/Discovery/AnnotatedClassDiscovery.php
@@ -12,7 +12,6 @@
 use Doctrine\Common\Annotations\AnnotationReader;
 use Doctrine\Common\Annotations\AnnotationRegistry;
 use Doctrine\Common\Reflection\StaticReflectionParser;
-use Doctrine\Common\Reflection\Psr0FindFile;
 use Drupal\Core\Annotation\Plugin;
 
 /**
@@ -55,7 +54,9 @@
           foreach ($directories as $fileinfo) {
             if ($fileinfo->getExtension() == 'php') {
               $className = str_replace(DIRECTORY_SEPARATOR, '\\', "$prefix/". $fileinfo->getBasename('.php'));
-              $staticReflectionParser = new StaticReflectionParser($className, new Psr0FindFile($namespaces));
+              $finder = new Psr0HintedFindFile($namespaces);
+              $finder->hint($className, $fileInfo->getPathName());
+              $staticReflectionParser = new StaticReflectionParser($className, $finder);
               if ($annotation = $reader->getClassAnnotation($staticReflectionParser->getReflectionClass(), 'Drupal\Core\Annotation\Plugin')) {
                 $definition = $annotation->get();
                 $definition['class'] = $reflectionClass->name;
only in patch2:
unchanged:
--- /dev/null
+++ b/core/lib/Drupal/Core/Plugin/Discovery/Psr0HintedFindFile.php
@@ -0,0 +1,34 @@
+<?php
+
+/**
+ * Definition of Drupal\Component\Plugin\Discovery\Psr0HintedFindFile.
+ */
+
+use Doctrine\Common\Reflection\Psr0FindFile;
+
+namespace Drupal\Core\Plugin\Discovery;
+
+class Psr0HintedFindFile extends Psr0FindFile {
+
+  /**
+   * Stores class => filename hints.
+   *
+   * @var array
+   */
+  protected $hints = array();
+
+  /**
+   * Tell the finder where to find a specific class.
+   */
+  function hint($class, $filename) {
+    $this->hints[$class] = $filename;
+    return $this;
+  }
+
+  /**
+   * Overrides Doctrine\Common\Reflection\Psr0FindFile::findFile().
+   */
+  function findFile($class) {
+    return isset($this->hints[$class]) ? $this->hints[$class] : parent::findFile($class);
+  }
+}