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
@@ -9,9 +9,10 @@
 
 use Drupal\Component\Plugin\Discovery\DiscoveryInterface;
 use Drupal\Core\Annotation\DirectoryIterator;
-use ReflectionClass;
 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;
 
 /**
@@ -53,8 +54,9 @@
           $directories = new DirectoryIterator($dir);
           foreach ($directories as $fileinfo) {
             if ($fileinfo->getExtension() == 'php') {
-              $reflectionClass = new ReflectionClass(str_replace(DIRECTORY_SEPARATOR, '\\', "$prefix/". $fileinfo->getBasename('.php')));
-              if ($annotation = $reader->getClassAnnotation($reflectionClass, 'Drupal\Core\Annotation\Plugin')) {
+              $className = str_replace(DIRECTORY_SEPARATOR, '\\', "$prefix/". $fileinfo->getBasename('.php'));
+              $staticReflectionParser = new StaticReflectionParser($className, new Psr0FindFile($namespaces));
+              if ($annotation = $reader->getClassAnnotation($staticReflectionParser->getReflectionClass(), 'Drupal\Core\Annotation\Plugin')) {
                 $definition = $annotation->get();
                 $definition['class'] = $reflectionClass->name;
                 $definitions[$definition['plugin_id']] = $definition;