rfkill command not found

I'm using Kali on my Raspberry pi I am trying to use airmon-ng but I'm getting the error

root@kali:~/downloads# airmon-ng
Your kernel supports rfkill but you don't have rfkill installed.

To ensure devices are unblocked you must install rfkill.

PHY     Interface       Driver          Chipset

null    wlan0           ??????          Realtek Semiconductor Corp. RTL8188CUS 802.11n WLAN Adapter

How do I install rfkill or how else would I avoid this error

I've tried sudo apt-get install rfkill and I got this error

root@kali:~# sudo apt-get install rfkill
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package rfkill

Running sudo apt-get update;sudo apt-get upgrade fixed the problem