diff --git a/Makefile b/Makefile
index 51fc08e..9527d12 100644
--- a/Makefile
+++ b/Makefile
@@ -7,6 +7,8 @@ include $(TOP)/config.mak
 VPATH = $(TOPSRC)
 CFLAGS += -I$(TOP)
 
+CFLAGS += $(CPPFLAGS)
+
 ifeq (-$(findstring gcc,$(CC))-,-gcc-)
  ifeq (-$(GCC_MAJOR)-$(findstring $(GCC_MINOR),56789)-,-4--)
   CFLAGS += -D_FORTIFY_SOURCE=0