reg: malformed auth challenge header error

Hello,

When I use curl or wget I can connect to our registry, e.g.,

$ curl -u myuser:mypass -D - https://docker.wyplay.com/v2/
HTTP/1.1 200 OK
Content-Length: 2
Content-Type: application/json; charset=utf-8
Docker-Distribution-Api-Version: registry/2.0
X-Content-Type-Options: nosniff
Date: Fri, 10 Mar 2017 16:16:05 GMT
{}

But when I use reg, I have the following error (with or without -k):

$ reg -d -u myuser -p mypass list 
2017/03/10 17:16:03 registry.ping url=https://docker.wyplay.com/v2/
Get https://docker.wyplay.com/v2/: malformed auth challenge header: 'Basic realm="Registry Realm"'
[...]

Do I need to modify something on the server? I am using a registry:2.5.1 image.