Luajit can't locate modules installed via Luarocks

Question

I'm to use a luarocks installed module with luajit but I get this error.

luajit-2.1.0-beta3: ./lex.lua:2: module 'lua-utf8' not found:
        no field package.preload['lua-utf8']
        no file './lua-utf8.lua'
        no file '/usr/local/share/luajit-2.1.0-beta3/lua-utf8.lua'
        no file '/usr/local/share/lua/5.1/lua-utf8.lua'
        no file '/usr/local/share/lua/5.1/lua-utf8/init.lua'
        no file './lua-utf8.so'
        no file '/usr/local/lib/lua/5.1/lua-utf8.so'
        no file '/usr/local/lib/lua/5.1/loadall.so'
stack traceback:
        [C]: in function 'require'
        ./lex.lua:2: in main chunk
        [C]: in function 'require'
        main.lua:1: in main chunk
        [C]: at 0x55fbf4106310

I've tried installing it with the --lua-version 5.1 flag but even then luajit doesn't seem to find the modules. How do I make luajit search for luarocks installed modules?