How do you set a static IP address for hosts that connect to a raspberry pi based wifi hot spot?

I'm looking to set static IP addresses for any device that connects to the pi via the wifi hotspot I created using hostapd and dnsmasq. How do you to this? Right now, it seems the IP may change after 24 hours of being disconnected - what's the correct way to ensure that any time a device connects to the pi using wlan0, it keeps that IP indefinitely?

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