diff --git a/share/mk/local.meta.sys.mk b/share/mk/local.meta.sys.mk
index 5e477885e1e2..decbb087870d 100644
--- a/share/mk/local.meta.sys.mk
+++ b/share/mk/local.meta.sys.mk
@@ -52,7 +52,7 @@ MACHINE_ARCH:= ${MACHINE_ARCH.${MACHINE}}
 # now because for universe we want to potentially
 # build for multiple MACHINE_ARCH per MACHINE
 # we need more than MACHINE in TARGET_SPEC
-TARGET_SPEC_VARS= MACHINE MACHINE_ARCH
+TARGET_SPEC_VARS?= MACHINE MACHINE_ARCH
 # see dirdeps.mk
 .if ${TARGET_SPEC:Uno:M*,*} != ""
 _tspec := ${TARGET_SPEC:S/,/ /g}