EXSLT set:distinct

Hello again XSLers,

I'm using Xalan 2.6 and when I use the EXSLT set:distinct() function 
with an exslt:node-set() result as a parameter I get a Java error:
XSLT Error (javax.xml.transform.TransformerException): 
org.apache.xml.utils.WrappedRuntimeException: 
java.lang.NoSuchMethodException: For extension function, could not find 
method org.apache.xml.utils.NodeVector.distinct([ExpressionContext,] ).
<xsl:for-each 
select="set:distinct(exslt:node-set($matched-items)/item)">
Is this right?

Cheers,
Richard