diff --git a/lib/behat/lib.php b/lib/behat/lib.php
index 1ca3f098be2..2608b37b9f7 100644
--- a/lib/behat/lib.php
+++ b/lib/behat/lib.php
@@ -220,7 +220,7 @@ function behat_clean_init_config() {
         'umaskpermissions', 'dbtype', 'dblibrary', 'dbhost', 'dbname', 'dbuser', 'dbpass', 'prefix',
         'dboptions', 'proxyhost', 'proxyport', 'proxytype', 'proxyuser', 'proxypassword',
         'proxybypass', 'theme', 'pathtogs', 'pathtodu', 'aspellpath', 'pathtodot', 'skiplangupgrade',
-        'altcacheconfigpath', 'pathtounoconv'
+        'altcacheconfigpath', 'pathtounoconv', 'alternative_file_system_class'
     ));
 
     // Add extra allowed settings.
diff --git a/lib/phpunit/bootstrap.php b/lib/phpunit/bootstrap.php
index 4927cc615f1..aa92af8e62a 100644
--- a/lib/phpunit/bootstrap.php
+++ b/lib/phpunit/bootstrap.php
@@ -186,7 +186,7 @@ $allowed = array('wwwroot', 'dataroot', 'dirroot', 'admin', 'directorypermission
                  'dbtype', 'dblibrary', 'dbhost', 'dbname', 'dbuser', 'dbpass', 'prefix', 'dboptions',
                  'proxyhost', 'proxyport', 'proxytype', 'proxyuser', 'proxypassword', 'proxybypass', // keep proxy settings from config.php
                  'altcacheconfigpath', 'pathtogs', 'pathtodu', 'aspellpath', 'pathtodot',
-                 'pathtounoconv'
+                 'pathtounoconv', 'alternative_file_system_class'
                 );
 $productioncfg = (array)$CFG;
 $CFG = new stdClass();