diff --git a/share/mk/doc.docbook.mk b/share/mk/doc.docbook.mk
index f8fac899a8..383b782446 100644
--- a/share/mk/doc.docbook.mk
+++ b/share/mk/doc.docbook.mk
@@ -1,5 +1,5 @@
 #
-# $FreeBSD: doc/share/mk/doc.docbook.mk,v 1.4 1999/12/13 18:14:41 nik Exp $
+# $FreeBSD: doc/share/mk/doc.docbook.mk,v 1.5 1999/12/24 01:25:27 nik Exp $
 #
 # This include file <doc.docbook.mk> handles building and installing of
 # DocBook documentation in the FreeBSD Documentation Project.
@@ -47,8 +47,8 @@ MASTERDOC?=	${.CURDIR}/${DOC}.sgml
 
 JADE=		${PREFIX}/bin/jade
 
-DSLHTML=	${DOC_PREFIX}/share/sgml/freebsd.dsl
-DSLPRINT=	${DOC_PREFIX}/share/sgml/freebsd.dsl
+DSLHTML?=	${DOC_PREFIX}/share/sgml/freebsd.dsl
+DSLPRINT?=	${DOC_PREFIX}/share/sgml/freebsd.dsl
 FREEBSDCATALOG=	${DOC_PREFIX}/share/sgml/catalog
 
 DOCBOOKCATALOG=	${PREFIX}/share/sgml/docbook/catalog