"Unknown escape sequence" error in Go

I have the following function written in Go. The idea is the function has a string passed to it and returns the first IPv4 IP address found. If no IP address is found, an empty string is returned.

func parseIp(checkIpBody string) string {
    reg, err := regexp.Compile("[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+")
    if err == nil {
        return ""
    }   
    return reg.FindString(checkIpBody)
}

The compile-time error I'm getting is

unknown escape sequence: .

How can I tell Go that the '.' is the actual character I'm looking for? I thought escaping it would do the trick, but apparently I'm wrong.