diff --git a/Makefile.inc1 b/Makefile.inc1
index bc004219f5da..11dd480a4f27 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -1899,7 +1899,7 @@ CD2ENV=${CDENV} CC="${CC} ${CD2CFLAGS}" \
 CDTMP=	${MAKEOBJDIRPREFIX}/${XDDIR}/${.CURDIR}/tmp
 CDMAKE=${CDENV} PATH=${CDTMP}/usr/bin:${PATH} ${MAKE} ${NOFUN}
 CD2MAKE=${CD2ENV} PATH=${CDTMP}/usr/bin:${XDDESTDIR}/usr/bin:${PATH} ${MAKE} ${NOFUN}
-XDDESTDIR=${DESTDIR}/${XDTP}
+XDDESTDIR?=${DESTDIR}/${XDTP}
 .if !defined(OSREL)
 OSREL!= uname -r | sed -e 's/[-(].*//'
 .endif