diff --git a/lib/lpc17xx/Makefile b/lib/lpc17xx/Makefile
index 126ad445..0317f6bc 100644
--- a/lib/lpc17xx/Makefile
+++ b/lib/lpc17xx/Makefile
@@ -24,7 +24,7 @@ PREFIX		?= arm-none-eabi
 
 CC		= $(PREFIX)-gcc
 AR		= $(PREFIX)-ar
-CFLAGS		= -O0 -g \
+CFLAGS		= -Os -g \
 		  -Wall -Wextra -Wimplicit-function-declaration \
 		  -Wredundant-decls -Wmissing-prototypes -Wstrict-prototypes \
 		  -Wundef -Wshadow \