New line does not work in UILabel

I want to add a carriage return on content of UILabel' text property:

myLabel.text = "Line1\nLine2"

On screen only "Line1" is displayed. I've already tested all the classic trick, i.e.:

myLabel.numberOfLines = 0

Now I made a test using Storyboard. Adding two UILabel with numberOfLines set to zero. On label 1, text is the previous one: "Line1\nLine2". On label 2 I used the ALT + RETURN keys to create carriage return. This can be achieve because text value is set using a dedicated field on StoryBoard.

Results: label 2 display the desired text but label 1.