diff --git a/nemu/tests/Makefile b/nemu/tests/Makefile
index fd12724..7709a27 100644
--- a/nemu/tests/Makefile
+++ b/nemu/tests/Makefile
@@ -1,6 +1,7 @@
 TEST_SRCS += tests/expr_test.c
 
 $(OBJ_DIR)/%: %.c $(TEST_OBJS) app
+	@mkdir -p $(dir $@)
 	@echo + CC $<
 	@$(CC) $(CFLAGS) -o $@.o -c $< 
 	@echo + LD $@