Strange calculation problem

[JPF]

I've hit a strange problem somewhere in my code and I narowed it down to
the following testcase:
----------------------
module test;
import tango.io.Stdout;

const ulong SIZE_IN_B = (1024 * 1024 * 1024 * 2); /*should be 2147483648*/
void main()
{
        Stdout.formatln("{0}", SIZE_IN_B); /*but is 18446744071562067968*/
}
----------------------

It happens with or without the parenthesis and without the const as well
. Am I doing something wrong, or did I just hit a bug?