Using ko.computed with a function returns readonly computed

I want readonly observables for my project, but the current definition for a computed returned from the 
<T>(func: () => T, context?: any, options?: any): KnockoutComputed<T>; overload is like an observable: 
(): T;
(value: T): void;

Supplying a value in this case will always throw an error, so I'd like to be explicit about it.