diff --git a/share/mk/src.sys.obj.mk b/share/mk/src.sys.obj.mk
index b5b27c36bfad..b2eeb3336cd5 100644
--- a/share/mk/src.sys.obj.mk
+++ b/share/mk/src.sys.obj.mk
@@ -43,7 +43,8 @@ MAKEOBJDIRPREFIX:=	${MAKEOBJDIRPREFIX}${TARGET:D/${TARGET}.${TARGET_ARCH}}
 # put things approximately where they want
 OBJROOT:=	${MAKEOBJDIRPREFIX}${SRCTOP}/
 MAKEOBJDIRPREFIX=
-.export MAKEOBJDIRPREFIX
+# export but do not track
+.export-env MAKEOBJDIRPREFIX
 .endif
 .if empty(MAKEOBJDIR)
 # OBJTOP set below