diff --git a/DOCS/xml/html-common.xsl b/DOCS/xml/html-common.xsl
index b62b3bc9ce..f21904cb53 100644
--- a/DOCS/xml/html-common.xsl
+++ b/DOCS/xml/html-common.xsl
@@ -8,7 +8,7 @@
      Set parameters
      ************** -->
 
-  <xsl:param name="toc.section.depth" select="'3'"/>
+  <xsl:param name="toc.section.depth" select="'4'"/>
 
   <xsl:param name="html.stylesheet" select="'default.css'"/>
   <xsl:param name="html.stylesheet.type" select="'text/css'"/>