diff --git a/install.php b/install.php
index 5416beb8f44..d23f4006f08 100644
--- a/install.php
+++ b/install.php
@@ -48,6 +48,7 @@ define('AJAX_SCRIPT', false); // prevents some warnings later
 define('CACHE_DISABLE_ALL', true); // Disables caching.. just in case.
 define('PHPUNIT_TEST', false);
 define('IGNORE_COMPONENT_CACHE', true);
+define('MDL_PERF_TEST', false);
 
 // Servers should define a default timezone in php.ini, but if they don't then make sure something is defined.
 // This is a quick hack.  Ideally we should ask the admin for a value.  See MDL-22625 for more on this.