diff --git a/tests/Bootstrap.php b/tests/Bootstrap.php
index 19c6a65a3..edc44c909 100644
--- a/tests/Bootstrap.php
+++ b/tests/Bootstrap.php
@@ -4,7 +4,7 @@
 \ini_set('display_errors', '1');
 \ini_set('display_startup_errors', '1');
 \error_reporting(\E_ALL);
-setlocale(LC_ALL, 'en_US.UTF-8');
+\setlocale(\LC_ALL, 'en_US.UTF-8');
 
 if (\is_file('vendor/autoload.php')) {
     include_once 'vendor/autoload.php';