diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
index 721c962..c079a5e 100644
--- a/DependencyInjection/Configuration.php
+++ b/DependencyInjection/Configuration.php
@@ -28,23 +28,17 @@ class Configuration implements ConfigurationInterface
                     ->children()
                         ->scalarNode('enabled')->defaultTrue()->end()
                         ->scalarNode('endpoint')->defaultValue('/app_dev.php')->end()
-                        ->scalarNode('json_declaration_method')
+                        ->enumNode('json_declaration_method')
+                            ->values(array('format_param', 'accept_header'))
                             ->defaultValue('format_param')
-                            ->validate()
-                                ->ifNotInArray(array('format_param', 'accept_header'))
-                                ->thenInvalid("Unknown json declaration method '%s'.")
-                            ->end()
                         ->end()
                         ->arrayNode('authentication')
                             ->children()
                                 ->scalarNode('name')->isRequired()->end()
-                                ->scalarNode('delivery')
+                                ->enumNode('delivery')
+                                    // header|query|request, but only query is implemented for now
+                                    ->values(array('query'))
                                     ->isRequired()
-                                    ->validate()
-                                        // header|query|request, but only query is implemented for now
-                                        ->ifNotInArray(array('query'))
-                                        ->thenInvalid("Unknown authentication delivery type '%s'.")
-                                    ->end()
                                 ->end()
                             ->end()
                         ->end()