diff --git a/xsl/html.xsl b/xsl/html.xsl
index e701b1a..6e03e27 100644
--- a/xsl/html.xsl
+++ b/xsl/html.xsl
@@ -39,6 +39,7 @@
   <xsl:param name="generate.section.toc.level" select="3"/>
   <xsl:param name="doc.standalone">false</xsl:param>
   <xsl:param name="chunker.output.indent">yes</xsl:param>
+  <xsl:param name="chunker.output.encoding">US-ASCII</xsl:param>
   <xsl:param name="chunk.quietly" select="not(number($boostbook.verbose))"/>
   <xsl:param name="toc.max.depth">2</xsl:param>
   <xsl:param name="callout.graphics.number.limit">15</xsl:param>