diff --git a/tests/php/bootstrap.php b/tests/php/bootstrap.php
index b04372f27..bb6789b07 100644
--- a/tests/php/bootstrap.php
+++ b/tests/php/bootstrap.php
@@ -11,7 +11,7 @@
 
 $_tests_dir = getenv( 'WP_TESTS_DIR' );
 if ( ! $_tests_dir ) {
-	$_tests_dir = '/tmp/wordpress-tests-lib';
+	$_tests_dir = rtrim( sys_get_temp_dir(), '/\\' ) . '/wordpress-tests-lib';
 }
 
 require_once $_tests_dir . '/includes/functions.php';