diff --git a/admin/settings/server.php b/admin/settings/server.php
index c9ca4e72821..5f47bcd3fc7 100644
--- a/admin/settings/server.php
+++ b/admin/settings/server.php
@@ -244,9 +244,10 @@ $ADMIN->add('server', new admin_externalpage('phpinfo', get_string('phpinfo'), "
 $temp = new admin_settingpage('performance', get_string('performance', 'admin'));
 
 $temp->add(new admin_setting_special_selectsetup('memorylimit', get_string('memorylimit', 'admin'),
-                                          get_string('configmemorylimit', 'admin'), '128M',
+                                          get_string('configmemorylimit', 'admin'), 0,
+                                          // if this option is set to 0, default 128M will be used
                                           array( '64M' => '64M',
-                                                 '128M' => '128M',
+                                                 '0' => '128M',
                                                  '256M' => '256M',
                                                  '1024M' => '1024M'
                                              )));