Changing internal nginx port has no effect


I have a first computer running nginx as a reverse-proxy which redirects requests towards to another comuter running gitlab-ce and its nginx, which is listening on port 80. I’d like that the nginx of gitlab-ce listens on another port than port 80.
I added nginx['listen_port'] = 8088 to my /etc/gitlab/gitlab.rb and ran gitlab-ctl reconfigure and even gitlab-ctl restart. However, nginx is still listening on port 80. What am I doing wrong?

Try changing only external_url in /etc/gitlab/gitlab.rb