How to invoke a class method using performSelector() on AnyClass in Swift?

In ObjC you could simply invoke a class method using the class method from NSObject.

[Machine performSelector:@selector(calculate:) withObject:num];

But how do you do this in Swift (2.2)?

@objc(Machine)
class Machine: NSObject {
    static func calculate(param: NSNumber) -> String {
        if param.integerValue > 5 {
            return "42"
        }
        return "42" // there is only 1 answer to all the questions :D
    }
}

if let aClass = NSClassFromString("Machine") {
    let sel = #selector(Machine.calculate(_:))
    let num = NSNumber(integer: 1337)
    let answer = aClass.performSelector(sel, withObject: num) // compiler error
    // let answer = aClass.calculate(num)                     // <-- this works
    print(answer)
}

With above code I'm getting the following compiler error:

error: cannot invoke 'performSelector' with an argument list of type '(Selector, withObject: NSNumber)'

What am I missing here?