"unknown flag -safe-string" on OCaml 5.0

[kit-ty-kate]

Using this project at this particular commit: kit-ty-kate/mastodon-archive-viewer@bd94f22 using OCaml 5.0.0~beta1
Then opening src/main.ml using emacs and reloading merlin will show the following error:

unknown flag -safe-string (0 pending errors, use C-c C-x to jump)

However the command is still around and works perfectly fine (it's no noop)