Problem with a Subd between a cylinder and rectangle

Hey Guys,
so i am modelling a piece of Furniture right now and got a problem that i couldn’t find an answer online. But its actually a simple problem.

I want the rectangle in the middle to keep its exact shape and top and bottom of the cylinder to be circles with hard corners. I got the second part right put the rectangle in the middle always changes to an oval. Creasing edges didn’t helped.

Here is the Rhino 7 file.
SubDShell.3dm (161.7 KB)

Thank you for your Help!

Hi Veterahn - you can select those faces and SubDivide or crease just the corner vertices


Or some of each…



Thank you Sir!