diff --git a/Resources/config/sundown.xml b/Resources/config/sundown.xml
index 84f3f87..ea1f81d 100644
--- a/Resources/config/sundown.xml
+++ b/Resources/config/sundown.xml
@@ -3,17 +3,23 @@
            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
            xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">
 
+    <parameters>
+        <parameter key="markdown.parser.sundown.class">Knp\Bundle\MarkdownBundle\Parser\SundownParser</parameter>
+        <parameter key="markdown.sundown.base_parser.class">Sundown\Markdown</parameter>
+        <parameter key="markdown.sundown.renderer.class">Sundown\Render\HTML</parameter>
+    </parameters>
+
     <services>
-        <service id="markdown.parser.sundown" class="Knp\Bundle\MarkdownBundle\Parser\SundownParser" public="false">
+        <service id="markdown.parser.sundown" class="%markdown.parser.sundown.class%" public="false">
             <argument type="service" id="markdown.sundown.base_parser" />
         </service>
 
-        <service id="markdown.sundown.base_parser" public="false" class="Sundown\Markdown">
+        <service id="markdown.sundown.base_parser" public="false" class="%markdown.sundown.base_parser.class%">
             <argument type="service" id="markdown.sundown.renderer" />
             <argument>%markdown.sundown.extensions%</argument>
         </service>
 
-        <service id="markdown.sundown.renderer" public="false" class="Sundown\Render\HTML">
+        <service id="markdown.sundown.renderer" public="false" class="%markdown.sundown.renderer.class%">
             <argument>%markdown.sundown.render_flags%</argument>
         </service>
     </services>