autocmd behaviour not as expected

I'm trying to set hlsearch on by default when I enter a buffer in vim.

Ruing :set hls manually upon entering a buffer performs the action I expect. However, when I add autocmd BufEnter * set hls to my .vimrc (and reload vim), nothing happens upon opening a buffer. Adding a colon in front of set doesn't change the behavior.

For context, I'm trying to use this script, but have it set "on" by default. I tried both of the tips mentioned in the "load at startup" section of the page with no success.

I removed everything else from my .vimrc, so it's not interference from something else.