Readonly has issues with intersection types

[johnfn]

TypeScript Version: 2.6.2

Code

class Foo<T, U> {
    thing(): Readonly<T> {
        return undefined as T;
    }

    erroringThing(): Readonly<T & U> {
        return undefined as T & U; // Type 'T & U' is not assignable to type 'Readonly<T & U>'.
    }
}

Expected behavior:
Both of these are error free.

Actual behavior:

Type 'T & U' is not assignable to type 'Readonly<T & U>'.

[mhegazy]

Should be fixed by #19564. give typescript@next a try.