programming the atmega1284 fuses

I am going to be programming this chip via Pololu ISP programmer . I want to use the external crystal oscillator do I need to program any fuses for this ?
I used atmel328 before brand new chip and I burned the bootloader and sketches on it via arduino and I didn't burn any fuses but the datasheet for atmega1284P is saying that by default internal clock is used which is only 1Mhz , I will be using 20Mhz crystal .