diff --git a/common.mk b/common.mk
index 43340615..820b6d44 100644
--- a/common.mk
+++ b/common.mk
@@ -102,7 +102,6 @@ $(BOOTROM_TARGETS): $(build_dir)/bootrom.%.img: $(TESTCHIP_RSRCS_DIR)/testchipip
 #########################################################################################
 # AG: must re-elaborate if cva6 sources have changed... otherwise just run firrtl compile
 $(FIRRTL_FILE) $(ANNO_FILE) &: $(SCALA_SOURCES) $(sim_files) $(SCALA_BUILDTOOL_DEPS) $(EXTRA_GENERATOR_REQS)
-	if [ -d $(OUT_DIR) ]; then rm -rf $(OUT_DIR); fi
 	mkdir -p $(build_dir)
 	$(call run_scala_main,$(SBT_PROJECT),$(GENERATOR_PACKAGE).Generator,\
 		--target-dir $(build_dir) \
diff --git a/fpga/Makefile b/fpga/Makefile
index d037833b..4ae4bb0f 100644
--- a/fpga/Makefile
+++ b/fpga/Makefile
@@ -94,10 +94,11 @@ SIM_FILE_REQS += \
 	$(ROCKETCHIP_RSRCS_DIR)/vsrc/EICG_wrapper.v
 
 # copy files but ignore *.h files in *.f (match vcs)
-$(sim_files): $(SIM_FILE_REQS) | $(OUT_DIR)
-	cp -f $^ $(OUT_DIR)
+$(sim_files): $(SIM_FILE_REQS) $(OUT_DIR)
+	rm -rf $(OUT_DIR)/*
+	cp -f $(SIM_FILE_REQS) $(OUT_DIR)
 	$(foreach file,\
-		$^,\
+		$(SIM_FILE_REQS),\
 		$(if $(filter %.h,$(file)),\
 			,\
 			echo "$(addprefix $(OUT_DIR)/, $(notdir $(file)))" >> $@;))
diff --git a/sims/vcs/Makefile b/sims/vcs/Makefile
index d407fe4f..3e78643d 100644
--- a/sims/vcs/Makefile
+++ b/sims/vcs/Makefile
@@ -38,10 +38,11 @@ SIM_FILE_REQS += \
 	$(ROCKETCHIP_RSRCS_DIR)/vsrc/TestDriver.v
 
 # copy files but ignore *.h files in *.f since vcs has +incdir+$(build_dir)
-$(sim_files): $(SIM_FILE_REQS) | $(OUT_DIR)
-	cp -f $^ $(OUT_DIR)
+$(sim_files): $(SIM_FILE_REQS) $(OUT_DIR)
+	rm -rf $(OUT_DIR)/*
+	cp -f $(SIM_FILE_REQS) $(OUT_DIR)
 	$(foreach file,\
-		$^,\
+		$(SIM_FILE_REQS),\
 		$(if $(filter %.h,$(file)),\
 			,\
 			echo "$(addprefix $(OUT_DIR)/, $(notdir $(file)))" >> $@;))
diff --git a/sims/verilator/Makefile b/sims/verilator/Makefile
index 5c15973a..269915a9 100644
--- a/sims/verilator/Makefile
+++ b/sims/verilator/Makefile
@@ -66,10 +66,11 @@ SIM_FILE_REQS += \
 	$(ROCKETCHIP_RSRCS_DIR)/csrc/remote_bitbang.cc
 
 # copy files and add -FI for *.h files in *.f
-$(sim_files): $(SIM_FILE_REQS) | $(OUT_DIR)
-	cp -f $^ $(OUT_DIR)
+$(sim_files): $(SIM_FILE_REQS) $(OUT_DIR)
+	rm -rf $(OUT_DIR)/*
+	cp -f $(SIM_FILE_REQS) $(OUT_DIR)
 	$(foreach file,\
-		$^,\
+		$(SIM_FILE_REQS),\
 		$(if $(filter %.h,$(file)),\
 			echo "-FI $(addprefix $(OUT_DIR)/, $(notdir $(file)))" >> $@;,\
 			echo "$(addprefix $(OUT_DIR)/, $(notdir $(file)))" >> $@;))
diff --git a/vlsi/Makefile b/vlsi/Makefile
index 228401b2..e699a476 100644
--- a/vlsi/Makefile
+++ b/vlsi/Makefile
@@ -108,10 +108,11 @@ SIM_FILE_REQS += \
 	$(ROCKETCHIP_RSRCS_DIR)/vsrc/TestDriver.v
 
 # copy files but ignore *.h files in *.f since vcs has +incdir+$(build_dir)
-$(sim_files): $(SIM_FILE_REQS) | $(build_dir)
-	cp -f $^ $(build_dir)
+$(sim_files): $(SIM_FILE_REQS) $(build_dir)
+	rm -rf $(build_dir)/*
+	cp -f $(SIM_FILE_REQS) $(build_dir)
 	$(foreach file,\
-		$^,\
+		$(SIM_FILE_REQS),\
 		$(if $(filter %.h,$(file)),\
 			,\
 			echo "$(addprefix $(build_dir)/, $(notdir $(file)))" >> $@;))