diff --git a/src/Symfony/Bridge/PhpUnit/bin/simple-phpunit b/src/Symfony/Bridge/PhpUnit/bin/simple-phpunit
index 2f97e32e11..a549cd7da4 100755
--- a/src/Symfony/Bridge/PhpUnit/bin/simple-phpunit
+++ b/src/Symfony/Bridge/PhpUnit/bin/simple-phpunit
@@ -26,8 +26,13 @@ if (PHP_VERSION_ID >= 70200) {
     $PHPUNIT_VERSION = '4.8';
 }
 
+if ('composer.json' !== $COMPOSER_JSON = getenv('COMPOSER') ?: 'composer.json') {
+    putenv('COMPOSER=composer.json');
+    $_SERVER['COMPOSER'] = $_ENV['COMPOSER'] = 'composer.json';
+}
+
 $root = __DIR__;
-while (!file_exists($root.'/composer.json') || file_exists($root.'/DeprecationErrorHandler.php')) {
+while (!file_exists($root.'/'.$COMPOSER_JSON) || file_exists($root.'/DeprecationErrorHandler.php')) {
     if ($root === dirname($root)) {
         break;
     }