Index: Makefile.in
--- Makefile.in.orig
+++ Makefile.in
@@ -197,6 +197,6 @@ Makefile: Makefile.in
 	    -e 's!@''dotlock@!$(DOTLOCKBASE)!' $@.in > $@
 
 %.o: %.c
-	$(CC) $(CFLAGS) $(DEFS) -c $<
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(DEFS) -c $<
 
 .PHONY: test test_perl update-version