diff --git a/tests/Bootstrap.php b/tests/Bootstrap.php
index 88df893..797e5b4 100644
--- a/tests/Bootstrap.php
+++ b/tests/Bootstrap.php
@@ -4,7 +4,7 @@ if (!file_exists('vendor/autoload.php')) {
     `composer dump-autoload`;
 }
 
-require './vendor/autoload.php';
+require __DIR__ . '/../vendor/autoload.php';
 
 if (!class_exists('PHPUnit\Framework\TestCase')) {
     // we run on an older PHPUnit version without namespaces.