diff --git a/Makefile b/Makefile
index 0c45ed0..9fa43b4 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ TARGET = vernam
 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 = vernam.c