There is a enum

public enum LockMode
        implements IntegerEnum
{
  Locked(0x00),
  Unlocked(0x04),
  Unknown(0xFF);

  ReaderMode(int aValue)
  {
    value = aValue;
  }

  @Override
  public int intValue()
  {
    return value;
  }

  private final int value;
}

But when it is used as value for Enum8 field of Struct there is an exception when the value is Unknown that says:

java.lang.IllegalArgumentException: No known Enum mapping for value -1 of type lock.LockMode

The problem is that Unknown field has value of 0xFF, which is -1 in byte equivalent.

I think, it would be better if jnr.ffi.util.EnumMapper will compare unsigned values.