diff --git a/npc/Makefile b/npc/Makefile
index 7748453..82d01f2 100644
--- a/npc/Makefile
+++ b/npc/Makefile
@@ -52,8 +52,8 @@ compile_commands.json: clean
 
 .PHONY: clean nvboard sim nvboard-bin sim-bin git_trace_sim git_trace_nvboard
 
-nvboard-bin: OBJDIR := $(PREFIX)/nvobj
-nvboard-bin: SUBMAKE := $(OBJDIR)/V$(CHISEL_TOP_MODULE).mk
+nvboard-bin: OBJDIR = $(PREFIX)/nvobj
+nvboard-bin: SUBMAKE = $(OBJDIR)/V$(CHISEL_TOP_MODULE).mk
 # TODO: fix this awkward way to find nvboard.a
 nvboard-bin: CPPSRCS := $(addprefix $(PWD)/,$(wildcard csrc_nvboard/*.cpp)) $(SRC_AUTO_BIND) $(NVBOARD_HOME)/build/nvboard.a
 nvboard-bin: CXXFLAGS += -I$(NVBOARD_HOME)/include $(shell sdl2-config --cflags)