diff --git a/index.xml b/index.xml
index 79f6535b7..794507954 100644
--- a/index.xml
+++ b/index.xml
@@ -4,7 +4,7 @@
   %general-entities;
 ]>
 <book>
-
+<!-- A dummy comment for email testing. -->
 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="prologue/bookinfo.xml"/>
 <!--
 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="prologue/dedication.xml"/>