--- a/Makefile	Fri Apr 11 14:42:10 2014 +0300
+++ b/Makefile	Fri Apr 11 14:42:19 2014 +0300
@@ -15,10 +15,11 @@
 
 # CPU clock frequency
 CPU = 16000000
+STD = c99
 
 CC = avr-gcc
 CPPFLAGS = -DF_CPU=$(CPU)UL
-CFLAGS = -g -mmcu=$(MCU) -Os
+CFLAGS = -mmcu=$(MCU) -std=$(STD) -Os -g
 
 build/%.elf: %.c
 	$(CC) $(CPPFLAGS) $(CFLAGS) -o $@ $*.c