diff --git a/data/xslt/xml2dot.xsl b/data/xslt/xml2dot.xsl
index 416ee13e..1d56ca8d 100644
--- a/data/xslt/xml2dot.xsl
+++ b/data/xslt/xml2dot.xsl
@@ -151,7 +151,7 @@
 </xsl:template>
 
 <xsl:template name="escape">
-  <xsl:param name="subject" required="yes"/>
+  <xsl:param name="subject"/> <!-- required -->
   <xsl:call-template name="string-replace">
     <xsl:with-param name="subject">
       <xsl:call-template name="string-replace">