[go-nuts] go get: unrecognized import path

I'm trying to install `golang.org/x/oauth2`, but I keep getting an error that I
don't understand at all:

     $ go get golang.org/x/oauth2
     package golang.org/x/oauth2: unrecognized import path "golang.org/x/oauth2"

My GOPATH is set properly, and I've been able to install other (eg: `go get
github.com/gorilla/mux`) without any issues.

Any hints?

     $ go version
     go version go1.4.1 linux/amd64

Thanks,