diff --git a/admin/cli/install.php b/admin/cli/install.php
index bcdaad9a1d9..ee5547eb05a 100644
--- a/admin/cli/install.php
+++ b/admin/cli/install.php
@@ -30,6 +30,7 @@
  */
 
 define('CLI_SCRIPT', true);
+define('NO_DEBUG_DISPLAY', false);
 
 // extra execution prevention - we can not just require config.php here
 if (isset($_SERVER['REMOTE_ADDR'])) {
diff --git a/install.php b/install.php
index fdc54da559e..7fc10dbddc4 100644
--- a/install.php
+++ b/install.php
@@ -46,6 +46,7 @@ if (file_exists($configfile)) {
 define('CLI_SCRIPT', false); // prevents some warnings later
 define('AJAX_SCRIPT', false); // prevents some warnings later
 define('CACHE_DISABLE_ALL', true); // Disables caching.. just in case.
+define('NO_DEBUG_DISPLAY', false);
 define('PHPUNIT_TEST', false);
 define('IGNORE_COMPONENT_CACHE', true);
 define('MDL_PERF_TEST', false);