`sudo su` from shell causes error

zsh is probably not the default shell on root, since running sudo su from user shell causes the following error:

$ sudo su
Error: Oh My Zsh can't be loaded from: bash. You need to run zsh instead.
Here's the process tree:

 PPID   PID COMMAND
    1  3651 tmux new -A -s /projects/project
 3651  3652  \_ -zsh
 3652  6661      \_ sudo su
 6661  6662          \_ su
 6662  6663              \_ bash

bash: spaceship: command not found