diff --git a/src/Behat/MinkExtension/ServiceContainer/Driver/Selenium2Factory.php b/src/Behat/MinkExtension/ServiceContainer/Driver/Selenium2Factory.php
index 1c72b4f..c5d28e6 100644
--- a/src/Behat/MinkExtension/ServiceContainer/Driver/Selenium2Factory.php
+++ b/src/Behat/MinkExtension/ServiceContainer/Driver/Selenium2Factory.php
@@ -98,7 +98,7 @@ class Selenium2Factory implements DriverFactory
                 ->scalarNode('platform')->end()
                 ->scalarNode('browserVersion')->end()
                 ->scalarNode('browser')->defaultValue('firefox')->end()
-                ->booleanNode('marionette')->defaultNull()->end()
+                ->booleanNode('marionette')->end()
                 ->booleanNode('ignoreZoomSetting')->defaultFalse()->end()
                 ->scalarNode('name')->defaultValue('Behat feature suite')->end()
                 ->scalarNode('deviceOrientation')->end()