# `popstate` called with empty state
#### Why This Error Occurred
When using the browser back button the popstate event is triggered. Next.js sees a
`popstate` event being triggered but `event.state` did not have `url` or `as`, causing a route change failure.
#### Possible Ways to Fix It
The only known cause of this issue is manually manipulating `window.history` instead of using `next/router`. Starting from version 9.5, Next.js will ignore `popstate` events that contain `event.state` not created by its own router.
### Useful Links
- [The issue this was reported in: #4994](https://github.com/vercel/next.js/issues/4994)
