Aside from using a safety pin, what are some ingenious ways to fix a buttoned shirt that's a bit too tight across the bust?

I have an awesome shirt that I’ve not yet worn because it’s a bit tight across the chest and that gap between buttonholes pulls apart. The shirt fits awesomely otherwise, and the stretching across the chest isn’t excessive, I just need that gap to stay closed.

I know I can use a safety pin, but I am wondering if anyone has figured out something more ingenious or elegant.