diff --git a/DependencyInjection/Factory/FtpAdapterFactory.php b/DependencyInjection/Factory/FtpAdapterFactory.php
index c26ff36..9501280 100644
--- a/DependencyInjection/Factory/FtpAdapterFactory.php
+++ b/DependencyInjection/Factory/FtpAdapterFactory.php
@@ -53,7 +53,7 @@ class FtpAdapterFactory implements AdapterFactoryInterface
                 ->booleanNode('passive')->defaultFalse()->end()
                 ->booleanNode('create')->defaultFalse()->end()
                 ->scalarNode('mode')
-                    ->defaultValue(FTP_ASCII)
+                    ->defaultValue(defined('FTP_ASCII') ? FTP_ASCII : null)
                     ->beforeNormalization()
                     ->ifString()
                     ->then(function($v) { return constant($v); })