Index: Makefile
===================================================================
--- Makefile
+++ Makefile
@@ -5,8 +5,8 @@
 #
 # universe            - *Really* build *everything* (buildworld and
 #                       all kernels on all architectures).  Define
-#                       MAKE_JUST_KERNELS to only build kernels,
-#                       MAKE_JUST_WORLDS to only build userland.
+#                       MAKE_JUST_KERNELS or WITHOUT_WORLDS to only build kernels,
+#                       MAKE_JUST_WORLDS or WITHOUT_KERNELS to only build userland.
 # tinderbox           - Same as universe, but presents a list of failed build
 #                       targets and exits with an error if there were any.
 # buildworld          - Rebuild *everything*, including glue to help do
@@ -104,6 +104,15 @@
 # For more information, see the build(7) manual page.
 #
 
+.if defined(UNIVERSE_TARGET) || defined(MAKE_JUST_WORLDS) || defined(WITHOUT_KERNELS)
+__DO_KERNEL=no
+.endif
+.if defined(UNIVERSE_TARGET) || defined(MAKE_JUST_KERNELS) || defined(WITHOUT_WORLDS)
+__DO_WORLD=no
+.endif
+__DO_WORLD?=yes
+__DO_KERNEL?=yes
+
 # This is included so CC is set to ccache for -V, and COMPILER_TYPE/VERSION
 # can be cached for sub-makes. We can't do this while still running on the
 # old fmake from FreeBSD 9.x or older, so avoid including it then to avoid
@@ -522,7 +531,7 @@
 .endfor
 
 .if defined(UNIVERSE_TARGET)
-MAKE_JUST_WORLDS=	YES
+WITHOUT_KERNELS=	yes
 .else
 UNIVERSE_TARGET?=	buildworld
 .endif
@@ -634,7 +643,7 @@
 .endfor
 .endif	# !make(targets)
 
-.if !defined(MAKE_JUST_KERNELS)
+.if ${__DO_WORLD} == "yes"
 universe_${target}_done: universe_${target}_worlds .PHONY
 .for target_arch in ${TARGET_ARCHES_${target}}
 universe_${target}_worlds: universe_${target}_${target_arch} .PHONY
@@ -658,9 +667,9 @@
 	    ${MAKEFAIL}))
 	@echo ">> ${target}.${target_arch} ${UNIVERSE_TARGET} completed on `LC_ALL=C date`"
 .endfor
-.endif # !MAKE_JUST_KERNELS
+.endif # ${__DO_WORLD} == "yes"
 
-.if !defined(MAKE_JUST_WORLDS)
+.if ${__DO_KERNELS} == "yes"
 universe_${target}_done: universe_${target}_kernels .PHONY
 universe_${target}_kernels: universe_${target}_worlds .PHONY
 universe_${target}_kernels: universe_${target}_prologue .MAKE .PHONY
@@ -673,7 +682,7 @@
 	fi
 	@cd ${.CURDIR}; ${SUB_MAKE} ${.MAKEFLAGS} TARGET=${target} \
 	    universe_kernels
-.endif # !MAKE_JUST_WORLDS
+.endif # ${__DO_KERNELS} == "yes"
 
 # Tell the user the worlds and kernels have completed
 universe_${target}: universe_${target}_done