**TypeScript Version:** 2.4.2 **Code** ```ts type Foo = Readonly<{ [n: number]: string; }>; type Bar = { readonly [n: number]: string; }; function foobar(): void { const x: Foo = { [0]: 'asdf', [1]: 'fdsa', [-1]: 'dddd', }; const y: Bar = { [0]: 'qwer', [1]: 'rewq', [-1]: 'eeee', }; const z: string = x[0] + y[0]; } ``` **Expected behavior:** No Error **Actual behavior:** Shows error `Element implicitly has an 'any' type because type 'Readonly<{ [n: number]: string; }>' has no index signature.` for `x[0]`.