diff --git a/hw/bsp/gr_citrus/board.mk b/hw/bsp/gr_citrus/board.mk
index 241c12bc5..39aef2e9f 100644
--- a/hw/bsp/gr_citrus/board.mk
+++ b/hw/bsp/gr_citrus/board.mk
@@ -10,22 +10,23 @@ CFLAGS += \
 # Cross Compiler for RX
 CROSS_COMPILE = rx-elf-
 
+RX_NEWLIB ?= 1
+
 ifeq ($(CMDEXE),1)
 OPTLIBINC="$(shell for /F "usebackq delims=" %%i in (`where rx-elf-gcc`) do echo %%~dpi..\rx-elf\optlibinc)"
 else
 OPTLIBINC=$(shell dirname `which rx-elf-gcc`)../rx-elf/optlibinc
 endif
 
-ifeq ($(RX_NEWLIB),0)
+ifeq ($(RX_NEWLIB),1)
+CFLAGS += -DSSIZE_MAX=__INT_MAX__
+else
 # setup for optlib
 CFLAGS += -nostdinc \
   -isystem $(OPTLIBINC) \
   -DLWIP_NO_INTTYPES_H
 
 LIBS += -loptc -loptm
-else
-# setup for newlib
-LIBS += -lm
 endif
 
 MCU_DIR = hw/mcu/renesas/rx63n