How to prevent NSToolbar overlapping NSViewController content?

I have a basic MacOS app with a toolbar and a view controller. I'm trying to perform some layout without constraints but when I try to position a subview in the top left corner it gets hidden under the toolbar.

Here's an example to demonstrate the problem (this just requires a default MacOS app with a storyboard). I've added -10 to the y position so the label peeks out.

class ViewController: NSViewController {

    let label = NSTextField()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(label)
        label.stringValue = "My Label"
    }

    override func viewDidLayout() {
        super.viewDidLayout()

        label.sizeToFit()
        label.frame = CGRect(x: 0,
                             y: view.bounds.maxY - 10,
                             width: label.bounds.width,
                             height: label.bounds.height)
    }
}

What am I doing wrong please? Is there a way to tell the toolbar to sit above the view controller's content rather that overlapping it?

Many thanks in advance!

label.frame.y is the bottom of the label and its height > 10.

label.frame = CGRect(x: 0,
                     y: view.bounds.maxY - label.frame.height,
                     width: label.frame.width,
                     height: label.frame.height)