Don't know if 'safety pin' means anything in American? Very small diaper pin?
I graduated a couple of Sundays ago into my slightly smaller workshirt but still had to have it pinned on the inside for when I sit down, to avoid a nasty gape.
When I put it on yesterday - no need for the safety pin!
That is a big woohoo for me, because my midsection apple is my worst point, fat or thin.