I believe there is a slight bug on lines 20-21 in the ViewController here... https://github.com/Arti3DPlayer/USBDeviceSwift/blob/master/CleanFlightSerialExample/CleanFlightSerialExample/ViewController.swift#L20-L21 Instead I think it should be ``` if (self.devices.count > 0 && self.devicesComboBox.indexOfSelectedItem > -1) { let device = self.devices[self.devicesComboBox.indexOfSelectedItem] ``` I'm new to Swift (and IOKit), so there may be a better way to do this.