diff --git a/Documentation/docbook.xsl b/Documentation/docbook.xsl
index 9a6912c641..da8b05b922 100644
--- a/Documentation/docbook.xsl
+++ b/Documentation/docbook.xsl
@@ -1,5 +1,8 @@
 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 		version='1.0'>
  <xsl:import href="http://docbook.sourceforge.net/release/xsl/current/html/docbook.xsl"/>
- <xsl:output method="html" encoding="UTF-8" indent="no" />
+ <xsl:output method="html"
+     encoding="UTF-8" indent="no"
+     doctype-public="-//W3C//DTD HTML 4.01//EN"
+     doctype-system="http://www.w3.org/TR/html4/strict.dtd" />
 </xsl:stylesheet>