diff --git a/v2/tools/xsltproc.jam b/v2/tools/xsltproc.jam
index 85aad1495..6306cfaf1 100644
--- a/v2/tools/xsltproc.jam
+++ b/v2/tools/xsltproc.jam
@@ -53,7 +53,7 @@ rule compute-xslt-flags ( target : properties * )
 }
 
 
-local rule .xsltproc ( target : source stylesheet : properties * : dirname : action )
+local rule .xsltproc ( target : source stylesheet : properties * : dirname ? : action )
 {   
     STYLESHEET on $(target) = $(stylesheet) ;
     FLAGS on $(target) = [ compute-xslt-flags $(target) : $(properties) ] ;