[x] bug report => search github for a similar issue or PR before submitting
[ ] feature request
[ ] support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

ERROR Error: ExpressionChangedAfterItHasBeenCheckedError: Expression has changed after it was checked. Previous value: '[object Object]'. Current value: 'NaN'.
    at viewDebugError (errors.ts:30) [angular]
    at expressionChangedAfterItHasBeenCheckedError (errors.ts:29) [angular]
    at checkBindingNoChanges (util.ts:145) [angular]
    at checkNoChangesNodeInline (view.ts:438) [angular]
    at checkNoChangesNode (view.ts:519) [angular]
    at debugCheckNoChangesNode (services.ts:387) [angular]
    at debugCheckRenderNodeFn (services.ts:330) [angular]
    at Object.eval [as updateRenderer] (AppComponent.html:1) [angular]
    at Object.debugUpdateRenderer [as updateRenderer] (services.ts:307) [angular]
    at checkNoChangesView (view.ts:368) [angular]
    at callViewAction (view.ts:694) [angular]
    at execComponentViewsAction (view.ts:644) [angular]
    at checkNoChangesView (view.ts:368) [angular]
    at callWithDebugContext (services.ts:645) [angular]

@Component({
  selector: 'my-app',
  template: `<h1>Hello {{ name$ | async }}</h1>`
})
export class AppComponent { 
  name$ = Observable.of(NaN); 
}

{{ something$ | async | customPipe }}