diff --git a/hw/dv/tools/dvsim/sim.mk b/hw/dv/tools/dvsim/sim.mk
index adceb0b..f64748f 100644
--- a/hw/dv/tools/dvsim/sim.mk
+++ b/hw/dv/tools/dvsim/sim.mk
@@ -17,7 +17,9 @@
 prep_tool_srcs:
 	@echo "[make]: prep_tool_srcs"
 	mkdir -p ${tool_srcs_dir}
+ifneq (${tool_srcs},)
 	${LOCK_TOOL_SRCS_DIR} "cp -Ru ${tool_srcs} ${tool_srcs_dir}/."
+endif
 
 pre_build: prep_tool_srcs
 	@echo "[make]: pre_build"
@@ -28,7 +30,9 @@
 
 gen_sv_flist: pre_build
 	@echo "[make]: gen_sv_flist"
+ifneq (${sv_flist_gen_cmd},)
 	cd ${build_dir} && ${sv_flist_gen_cmd} ${sv_flist_gen_opts}
+endif
 
 build_tb: gen_sv_flist
 	@echo "[make]: build the testbench"