diff --git a/Makefile b/Makefile
index 4a9a447..68b7447 100644
--- a/Makefile
+++ b/Makefile
@@ -29,7 +29,7 @@ dirs-y = src
 cc-option=$(shell if test -z "`$(1) $(2) -S -o /dev/null -xc /dev/null 2>&1`" \
     ; then echo "$(2)"; else echo "$(3)"; fi ;)
 
-CFLAGS := -I$(OUT) -Isrc -I$(OUT)board-generic/ -std=gnu11 -O2 -MD -g \
+CFLAGS := -I$(OUT) -Isrc -I$(OUT)board-generic/ -std=gnu11 -Os -MD -g \
     -Wall -Wold-style-definition $(call cc-option,$(CC),-Wtype-limits,) \
     -ffunction-sections -fdata-sections
 CFLAGS += -flto -fwhole-program -fno-use-linker-plugin