diff --git a/firmware/src/Makefile b/firmware/src/Makefile
index f792d8e..6c80b72 100644
--- a/firmware/src/Makefile
+++ b/firmware/src/Makefile
@@ -2,6 +2,7 @@
 
 MCU := atmega328p
 PROGRAMMER := usbasp
+SPEED := 8000000UL
 
 TARGET := main.hex
 BIN := main.elf
@@ -13,7 +14,7 @@ OBJCOPY := avr-objcopy
 SIZE := avr-size
 AVRDUDE := avrdude
 
-CFLAGS := -mmcu=$(MCU) -Os -Wall -Werror -Wextra
+CFLAGS := -mmcu=$(MCU) -D F_CPU=$(SPEED) -Os -Wall -Werror -Wextra
 
 all: $(TARGET)
 
diff --git a/firmware/src/main.c b/firmware/src/main.c
index 97b51f2..f70b58d 100644
--- a/firmware/src/main.c
+++ b/firmware/src/main.c
@@ -1,5 +1,3 @@
-#define	F_CPU 8000000UL
-
 #include <avr/io.h>
 #include <avr/interrupt.h>
 #include <util/delay.h>