diff --git a/flow/Makefile b/flow/Makefile
index efe3aa4670..d06b31dcdf 100644
--- a/flow/Makefile
+++ b/flow/Makefile
@@ -394,7 +394,7 @@ do-klayout_tech:
 	cp $(TECH_LEF) $(OBJECTS_DIR)/klayout_tech.lef
 
 KLAYOUT_ENV_VAR_IN_PATH_VERSION = 0.28.11
-KLAYOUT_VERSION = $(shell $(KLAYOUT_CMD) -v 2>/dev/null | grep 'KLayout' | cut -d ' ' -f2)
+KLAYOUT_VERSION = $(if $(KLAYOUT_CMD),shell $(KLAYOUT_CMD) -v 2>/dev/null | grep 'KLayout' | cut -d ' ' -f2,))
 
 KLAYOUT_ENV_VAR_IN_PATH = $(shell \
 	if [ -z "$(KLAYOUT_VERSION)" ]; then \