Index: /usr/src/sys/conf/kern.post.mk
===================================================================
--- /usr/src/sys/conf/kern.post.mk	(revision 346308)
+++ /usr/src/sys/conf/kern.post.mk	(working copy)
@@ -75,6 +75,7 @@
 .endif
 # Keep the related ports builds in the obj directory so that they are only rebuilt once per kernel build
 WRKDIRPREFIX?=	${.OBJDIR}
+MAKEFLAGS_PORTS=${MAKEFLAGS:M*:tW:S/^-m /-m_/g:S/ -m / -m_/g:S/^-j /-m_/g:S/ -j / -m_/g:S/^-J /-m_/g:S/ -J / -m_/g:tw:N-m_*:NMK_AUTO_OBJ=*}
 PORTSMODULESENV=\
 	env \
 	-u CC \
@@ -83,7 +84,8 @@
 	-u MAKESYSPATH \
 	-u MK_AUTO_OBJ \
 	-u MAKEOBJDIR \
-	MAKEFLAGS="${MAKEFLAGS:M*:tW:S/^-m /-m_/g:S/ -m / -m_/g:tw:N-m_*:NMK_AUTO_OBJ=*}" \
+	MAKEFLAGS="${MAKEFLAGS_PORTS}" \
+	MAKE_JOBS_NUMBER=${.MAKE.JOBS} \
 	SYSDIR=${SYSDIR} \
 	PATH=${PATH}:${LOCALBASE}/bin:${LOCALBASE}/sbin \
 	SRC_BASE=${SRC_BASE} \
@@ -95,7 +97,7 @@
 all:
 .for __i in ${PORTS_MODULES}
 	@${ECHO} "===> Ports module ${__i} (all)"
-	cd $${PORTSDIR:-/usr/ports}/${__i}; ${PORTSMODULESENV} ${MAKE} -B clean build
+	${PORTSMODULESENV} ${MAKE} -C "$${PORTSDIR:-/usr/ports}/${__i}" clean build
 .endfor
 
 .for __target in install reinstall clean
@@ -103,7 +105,8 @@
 ports-${__target}:
 .for __i in ${PORTS_MODULES}
 	@${ECHO} "===> Ports module ${__i} (${__target})"
-	cd $${PORTSDIR:-/usr/ports}/${__i}; ${PORTSMODULESENV} ${MAKE} -B ${__target:C/(re)?install/deinstall reinstall/}
+	${PORTSMODULESENV} ${MAKE} -C "$${PORTSDIR:-/usr/ports}/${__i}" \
+	    ${__target:C/(re)?install/deinstall reinstall/}
 .endfor
 .endfor
 .endif