DateComponentsFormatter doesn't allow fractional units

Question

I can't make DateComponentsFormatter print out fractional units!

Here's the code in Swift 4:

let duration = 5400   // 1.5 hours in seconds

let dateComponentsFormatter = DateComponentsFormatter.init()
dateComponentsFormatter.allowedUnits = [.hour]
dateComponentsFormatter.maximumUnitCount = 1
dateComponentsFormatter.allowsFractionalUnits = true
dateComponentsFormatter.unitsStyle = .short

let stringDuration = dateComponentsFormatter.string(from: number)
print(stringDuration!)

I've played around with allowedUnits and maximumUnitCount, but I can only make it print "1 hr" or "2 hrs".

How do I make in print "1.5 hrs"?