TypeError: Cannot read property 'transform' of undefined

[ghost]

I receive TypeError: Cannot read property 'transform' of undefined when trying to compile any code that follows this pattern:

while( true ) {
    let foo = 1;
    ( () => { foo; } )();
}

It seems to involve the following components:

1. while loop (for loops seem unaffected)
2. variable declared within loop using either let or const (var is fine)
3. variable created in 2 is referenced inside a closure within the loop

I understand this code might be buggy or bad practice, but the error from Traceur is cryptic.

I am compiling using traceur v0.0.90 via grunt-traceur v0.5.4.

[ghost]

@arv Wow! You fixed that fast!

[arv]

...because I'm addicted to the "Wow!"s