diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 2664a42..145c6b0 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2140,6 +2140,10 @@ function _drupal_bootstrap_configuration() {
     // All Symfony-borrowed code lives in /core/vendor/Symfony.
     'Symfony' => DRUPAL_ROOT . '/core/vendor',
   ));
+  $loader->registerPrefixes(array(
+    // All PEAR-borrowed code lives in /core/vendor/PEAR.
+    'Archive_Tar' => DRUPAL_ROOT . '/core/vendor/PEAR',
+  ));
   // Register the Drupal namespace for classes in core as a fallback.
   // This allows to register additional namespaces within the Drupal namespace
   // (e.g., for modules) and avoids an additional file_exists() on the Drupal
diff --git a/core/lib/Drupal/Component/Archiver/Tar.php b/core/lib/Drupal/Component/Archiver/Tar.php
index c1d8bd0..374133e 100644
--- a/core/lib/Drupal/Component/Archiver/Tar.php
+++ b/core/lib/Drupal/Component/Archiver/Tar.php
@@ -7,7 +7,7 @@
 
 namespace Drupal\Component\Archiver;
 
-use PEAR\Archive_Tar\Archive_Tar;
+use Archive_Tar;
 
 /**
  * Defines a archiver implementation for .tar files.