installing multisite (sub dom) in root with other single installs

Hi I think I know the answer to this but not really I'd like to install a fresh WP multisite on a root that already has some directories with other sites in it, but they're all single installs. My fear is that when I go to do this, WP will tell me "You've already got sub-directories here, so you can only have a sub-directory multisite." Will this happen? Thanks.