diff --git a/tests/phpunit/includes/install.php b/tests/phpunit/includes/install.php
index 7081302d68..82d53226a3 100644
--- a/tests/phpunit/includes/install.php
+++ b/tests/phpunit/includes/install.php
@@ -9,6 +9,7 @@ error_reporting( E_ALL & ~E_DEPRECATED & ~E_STRICT );
 $config_file_path = $argv[1];
 $multisite = ! empty( $argv[2] );
 
+define( 'WP_INSTALLING', true );
 require_once $config_file_path;
 require_once dirname( __FILE__ ) . '/functions.php';