How to fix "zsh compinit: insecure directories"?

This made the error go away:

cd /usr/local/share/zsh
sudo chmod -R 755 ./site-functions
sudo chown -R root:root ./site-functions

I'm still unsure what the error meant or why it happened, though.

Credit: this answer on StackOverflow which in turn got the solution from a post on the zsh mailing list