diff --git a/src/collective/dms/mailcontent/profiles/default/catalog.xml b/src/collective/dms/mailcontent/profiles/default/catalog.xml
index 602cb01..1a3c8cf 100644
--- a/src/collective/dms/mailcontent/profiles/default/catalog.xml
+++ b/src/collective/dms/mailcontent/profiles/default/catalog.xml
@@ -4,6 +4,10 @@
         <indexed_attr value="internal_reference_number"/>
     </index>
     <column value="internal_reference_number"/>
+    <index name="order_number" meta_type="FieldIndex">
+        <indexed_attr value="order_number"/>
+    </index>
+    <column value="order_number"/>
     <index name="reception_date" meta_type="DateIndex">
         <indexed_attr value="reception_date"/>
     </index>