diff --git a/phpBB/install.php b/phpBB/install.php
index 0b98275205..4633b30d6b 100644
--- a/phpBB/install.php
+++ b/phpBB/install.php
@@ -869,6 +869,7 @@ else
 		//
 		if ( $upgrade == 1 && $upgrade_now == $lang['upgrade_submit'] )
 		{
+			define('INSTALLING', true);
 			require('upgrade.'.$phpEx);
 			exit;
 		}