Enum defined in C++ with -1 is undefined in QML

C++ CODE:
class MyClass : QObject {
Q_OBJECT
    enum MyEnum {
        Invalid = -1,
        Valid1,
        Valid2
    }
    Q_ENUMS( MyEnum )
};

QML CODE:

function check() {
    console.log( typeof( MyClass.Invalid ) ); // Returns "undefined"
    console.log( typeof( MyClass.Valid1 ) ); // Returns "number" as expected
}