diff --git a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/default.phpt b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/default.phpt
index cd733724870cd..db60e3d25076e 100644
--- a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/default.phpt
+++ b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/default.phpt
@@ -12,8 +12,12 @@ $vendor = __DIR__;
 while (!file_exists($vendor.'/vendor')) {
     $vendor = dirname($vendor);
 }
-define('PHPUNIT_COMPOSER_INSTALL', $vendor.'/vendor/autoload.php');
-require PHPUNIT_COMPOSER_INSTALL;
+// Fake class to ensure bootstrap.php calls DeprecationErrorHandler::register().
+class PHPUnit_TextUI_Command
+{
+
+}
+require  $vendor.'/vendor/autoload.php';
 require_once __DIR__.'/../../bootstrap.php';
 
 @trigger_error('root deprecation', E_USER_DEPRECATED);
diff --git a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/disabled.phpt b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/disabled.phpt
index 0115bbd24259a..b2aa84f3b84d7 100644
--- a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/disabled.phpt
+++ b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/disabled.phpt
@@ -12,8 +12,12 @@ $vendor = __DIR__;
 while (!file_exists($vendor.'/vendor')) {
     $vendor = dirname($vendor);
 }
-define('PHPUNIT_COMPOSER_INSTALL', $vendor.'/vendor/autoload.php');
-require PHPUNIT_COMPOSER_INSTALL;
+// Fake class to ensure bootstrap.php calls DeprecationErrorHandler::register().
+class PHPUnit_TextUI_Command
+{
+
+}
+require  $vendor.'/vendor/autoload.php';
 require_once __DIR__.'/../../bootstrap.php';
 
 echo (int) set_error_handler('var_dump');
diff --git a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/regexp.phpt b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/regexp.phpt
index 3b7207b85f8ee..2bea6d3bb5fcb 100644
--- a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/regexp.phpt
+++ b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/regexp.phpt
@@ -12,8 +12,12 @@ $vendor = __DIR__;
 while (!file_exists($vendor.'/vendor')) {
     $vendor = dirname($vendor);
 }
-define('PHPUNIT_COMPOSER_INSTALL', $vendor.'/vendor/autoload.php');
-require PHPUNIT_COMPOSER_INSTALL;
+// Fake class to ensure bootstrap.php calls DeprecationErrorHandler::register().
+class PHPUnit_TextUI_Command
+{
+
+}
+require  $vendor.'/vendor/autoload.php';
 require_once __DIR__.'/../../bootstrap.php';
 
 @trigger_error('root deprecation', E_USER_DEPRECATED);
diff --git a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak.phpt b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak.phpt
index 9e78d96e70efb..e65cd8648dfc0 100644
--- a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak.phpt
+++ b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak.phpt
@@ -12,8 +12,12 @@ $vendor = __DIR__;
 while (!file_exists($vendor.'/vendor')) {
     $vendor = dirname($vendor);
 }
-define('PHPUNIT_COMPOSER_INSTALL', $vendor.'/vendor/autoload.php');
-require PHPUNIT_COMPOSER_INSTALL;
+// Fake class to ensure bootstrap.php calls DeprecationErrorHandler::register().
+class PHPUnit_TextUI_Command
+{
+
+}
+require  $vendor.'/vendor/autoload.php';
 require_once __DIR__.'/../../bootstrap.php';
 
 @trigger_error('root deprecation', E_USER_DEPRECATED);
diff --git a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak_vendors_on_non_vendor.phpt b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak_vendors_on_non_vendor.phpt
index 7568d54a9ce91..a56db364171b2 100644
--- a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak_vendors_on_non_vendor.phpt
+++ b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak_vendors_on_non_vendor.phpt
@@ -12,8 +12,12 @@ $vendor = __DIR__;
 while (!file_exists($vendor.'/vendor')) {
     $vendor = dirname($vendor);
 }
-define('PHPUNIT_COMPOSER_INSTALL', $vendor.'/vendor/autoload.php');
-require PHPUNIT_COMPOSER_INSTALL;
+// Fake class to ensure bootstrap.php calls DeprecationErrorHandler::register().
+class PHPUnit_TextUI_Command
+{
+
+}
+require  $vendor.'/vendor/autoload.php';
 require_once __DIR__.'/../../bootstrap.php';
 
 @trigger_error('root deprecation', E_USER_DEPRECATED);
diff --git a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak_vendors_on_vendor.phpt b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak_vendors_on_vendor.phpt
index 7e9c6f8ed7682..f43ebde4929b7 100644
--- a/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak_vendors_on_vendor.phpt
+++ b/src/Symfony/Bridge/PhpUnit/Tests/DeprecationErrorHandler/weak_vendors_on_vendor.phpt
@@ -12,8 +12,12 @@ $vendor = __DIR__;
 while (!file_exists($vendor.'/vendor')) {
     $vendor = dirname($vendor);
 }
-define('PHPUNIT_COMPOSER_INSTALL', $vendor.'/vendor/autoload.php');
-require PHPUNIT_COMPOSER_INSTALL;
+// Fake class to ensure bootstrap.php calls DeprecationErrorHandler::register().
+class PHPUnit_TextUI_Command
+{
+
+}
+require  $vendor.'/vendor/autoload.php';
 require_once __DIR__.'/../../bootstrap.php';
 require __DIR__.'/fake_vendor/autoload.php';
 require __DIR__.'/fake_vendor/acme/lib/deprecation_riddled.php';
diff --git a/src/Symfony/Bridge/PhpUnit/bootstrap.php b/src/Symfony/Bridge/PhpUnit/bootstrap.php
index 2803caf02bcae..570eb97389a9e 100644
--- a/src/Symfony/Bridge/PhpUnit/bootstrap.php
+++ b/src/Symfony/Bridge/PhpUnit/bootstrap.php
@@ -13,7 +13,7 @@
 use Symfony\Bridge\PhpUnit\DeprecationErrorHandler;
 
 // Detect if we're loaded by an actual run of phpunit
-if (!defined('PHPUNIT_COMPOSER_INSTALL') && !class_exists('PHPUnit_TextUI_Command', false) && !class_exists('PHPUnit\TextUI\Command', false)) {
+if (!class_exists('PHPUnit_TextUI_Command', false) && !class_exists('PHPUnit\TextUI\Command', false)) {
     if ($ser = getenv('SYMFONY_DEPRECATIONS_SERIALIZE')) {
         DeprecationErrorHandler::collectDeprecations($ser);
     }