diff --git a/Makefile b/Makefile
index a72b365..677df1c 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ TARGET = nsh
 PREFIX ?= /usr/local
 BINDIR = $(PREFIX)/bin
 
-CFLAGS = -O3 -march=native -mtune=native -pipe -s -std=c99 -pedantic -Wall
+CFLAGS = -Os -march=native -mtune=native -pipe -s -std=c99 -pedantic -Wall
 
 SRC = nsh.c