diff --git a/src/Symfony/Bridge/PhpUnit/bootstrap.php b/src/Symfony/Bridge/PhpUnit/bootstrap.php
index b25891538d..91504ae4a8 100644
--- a/src/Symfony/Bridge/PhpUnit/bootstrap.php
+++ b/src/Symfony/Bridge/PhpUnit/bootstrap.php
@@ -4,7 +4,7 @@ use Doctrine\Common\Annotations\AnnotationRegistry;
 use Symfony\Bridge\PhpUnit\DeprecationErrorHandler;
 
 // Detect if we're loaded by an actual run of phpunit
-if (!class_exists('PHPUnit_TextUI_Command', false)) {
+if (!defined('PHPUNIT_COMPOSER_INSTALL') && !class_exists('PHPUnit_TextUI_Command', false)) {
     return;
 }