diff --git a/reference/mongo/mongocollection/aggregate.xml b/reference/mongo/mongocollection/aggregate.xml
index 17be842531..ede89355b7 100644
--- a/reference/mongo/mongocollection/aggregate.xml
+++ b/reference/mongo/mongocollection/aggregate.xml
@@ -75,6 +75,7 @@
    </para>
    <programlisting role="php">
 <![CDATA[
+<?php
 $m = new Mongo;
 $c = $m->selectDB("examples")->selectCollection("article");
 $c->drop();
@@ -110,13 +111,14 @@ $ops = array(
     array('$unwind' => '$tags'),
     array(
         '$group' => array(
-            "_id" => array("tags" => 1),
+            "_id" => array("tags" => '$tags'),
             "authors" => array('$addToSet' => '$author'),
         ),
     ),
 );
 $results = $c->aggregate($ops);
 var_dump($results);
+?>
 ]]>
    </programlisting>
    &example.outputs;