diff --git a/README.md b/README.md
index 4d22011..68bac07 100644
--- a/README.md
+++ b/README.md
@@ -41,6 +41,9 @@ Docker Compose installation options.
 
 (Used only for Debian/Ubuntu.) You can switch the channel to `edge` if you want to use the Edge release.
 
+You can change `docker_apt_gpg_key` to a different url if you are behind a firewall or provide a trustworthy mirror.
+Usually in combination with changing `docker_apt_repository` as well.
+
     docker_yum_repo_url: https://download.docker.com/linux/centos/docker-{{ docker_edition }}.repo
     docker_yum_repo_enable_edge: '0'
     docker_yum_repo_enable_test: '0'
@@ -48,6 +51,9 @@ Docker Compose installation options.
 
 (Used only for RedHat/CentOS.) You can enable the Edge or Test repo by setting the respective vars to `1`.
 
+You can change `docker_yum_gpg_key` to a different url if you are behind a firewall or provide a trustworthy mirror.
+Usually in combination with changing `docker_yum_repository` as well.
+
     docker_users:
       - user1
       - user2