diff --git a/vpi/Makefile b/vpi/Makefile
index ba6abe9f5..9150f2539 100644
--- a/vpi/Makefile
+++ b/vpi/Makefile
@@ -1,12 +1,13 @@
 CC=clang
 INSTDIR=/usr/lib/ivl
+INCDIRS=
 
 OBJ=ipc.o main.o
 
 all: migensim.vpi
 
 %.o: %.c
-	$(CC) -fPIC -Wall -O2 -c -o $@ $<
+	$(CC) -fPIC -Wall -O2 -c $(INCDIRS) -o $@ $<
 
 migensim.vpi: $(OBJ)
 	$(CC) -shared -o $@ $(OBJ) -lvpi