HostRegexp invalid?

Receiving this error when setting a frontend up in VulcanD:
> route should be a valid route expression

Here's the route im attempting to add:

```
frontend upsert --backend mockbin --id=mockbin --route 'HostRegexp("^mockbin\..*")'
```

I verified my regex using Rubular: http://rubular.com/r/qQiGivbXQ4

Thoughts?