Minimum scale factor for title of UIButton does not apply

Question

This is my text in side of a UIButton:

It should says "highscores", but it is okay now since it is in Storyboard and not running. My constrains are as followed:

The proportional width is 0.3 of the superview. I settled this in my viewDidLoad:

highscoresButton.titleLabel!.minimumScaleFactor = 0.5

But the simulator shows exactly the same as the storyboard. When applying a minimum scale factor for UILabels it works correctly. What am I doing wrong here? Thank you. Changing the minimum scale factor to 0.1 has also no effect.