packing of UInt16 not working

[tcurdt]

        let foo : UInt16 = 0
        let d = pack(">H", [ foo ])
        print(d)

gives at

            case "H":
                bytes = UInt16(truncatingBitPattern:o as! Int).data.bytes

Could not cast value of type 'Swift.UInt16' (0x110c130a0) to 'Swift.Int' (0x110c13618).