diff --git a/Makefile b/Makefile
index 3f0d754cc498..14267ce32f9e 100644
--- a/Makefile
+++ b/Makefile
@@ -86,8 +86,9 @@ TGTS+=	${BITGTS}
 
 PATH=	/sbin:/bin:/usr/sbin:/usr/bin
 MAKEOBJDIRPREFIX?=	/usr/obj
-_MAKEOBJDIRPREFIX!= /usr/bin/env -i PATH=${PATH} ${MAKE} ${.MAKEFLAGS} \
-		-f /dev/null -V MAKEOBJDIRPREFIX dummy
+_MAKEOBJDIRPREFIX!= /usr/bin/env -i PATH=${PATH} ${MAKE} \
+    ${.MAKEFLAGS:MMAKEOBJDIRPREFIX=*} \
+    -f /dev/null -V MAKEOBJDIRPREFIX dummy
 .if !empty(_MAKEOBJDIRPREFIX)
 .error MAKEOBJDIRPREFIX can only be set in environment, not as a global\
 	(in /etc/make.conf) or command-line variable.