diff --git a/ch4/os/Makefile b/ch4/os/Makefile
index 834beb3..f2c534f 100644
--- a/ch4/os/Makefile
+++ b/ch4/os/Makefile
@@ -26,7 +26,7 @@ $(KERNEL_BIN): build_elf
 	@$(OBJCOPY) $(KERNEL_ELF) --strip-all -O binary $@
 
 
-debug:build_elf $(KERNEL_BIN) $(SYMBOL_MAP)
+debug:build_elf $(KERNEL_BIN) $(SYMBOL_MAP) kill
 	$(QEMU_CMD_PATH) \
 		-machine virt \
 		-display none \