Prometheus HTTPS access error: ERR_SSL_PROTOCOL_ERROR (Chrome)

I can't access the Prometheus Dashboard under <your_domain_name>:9090 or <your_domain_name>:9100/metric because of an SSL protocol error.

I just installed the latest version of GitLab (8.16) and activated the Prometheus feature via /etc/gitlab/gitlab.rb:

prometheus['enable'] = true
node_exporter['enable'] = true

Following a sudo gitlab-ctl reconfigure.

When I try to access the dashboard Google Chrome responds with a ERR_SSL_PROTOCOL_ERROR.

We use Let's Encrypt certificates for our GitLab instance.

Are there any certificate options available for Prometheus?