Associative Array of Const Objects?

[bitwise via Digitalmars-d-learn]

class Test{}

void main()
{
        const(Test)[string] tests;
        tests["test"] = new Test();
}
This code used to work, but after upgrading to dmd 2.067, it no 
longer does.
--Error: cannot modify const expression tests["test"]

How do I insert an item into an associative array of const 
objects?