diff --git a/content/develop/contributing.md b/content/develop/contributing.md
index b25b243b9e9f81995364fcf65cb966be8b0708b0..8d7607e850ca6bda743a741e62712caa1208e8fe 100644
--- a/content/develop/contributing.md
+++ b/content/develop/contributing.md
@@ -72,7 +72,9 @@ Please avoid:
 
 ### Publish your work
 
-You are allowed to push directly on Arkindex's repositories, except for the `master` branch. The goal is for your code to be merged into `master` once the following steps are completed:
+External contributors cannot push directly on Arkindex's repositories. You will need to create a fork of the repository under your own namespace, then open a Merge Request on the original repository. To learn more, check out GitLab's [forking workflow documentation](https://docs.gitlab.com/ee/user/project/repository/forking_workflow.html).
+
+The goal is for your code to be merged into `master` once the following steps are completed:
 
 1. unit tests are all OK, meaning that all jobs in the CI stage named `test` ended in success
 2. formatting has been validated by a tool, meaning that all jobs in the CI stage named `checks` ended in success
@@ -84,6 +86,7 @@ When pushing [your code from your local branch](https://docs.gitlab.com/ee/user/
 
 Once your work is ready, configure your Merge Request as follows:
 
+- Make sure you are requesting a merge to the `master` branch of the upstream repository, not of your own fork.
 - Assign yourself as the **Assignee**.
 - Assign [@erouchet](https://gitlab.teklia.com/erouchet) as the **Reviewer**: he will either review or re-assign to another reviewer when needed.
 - Set an explicit name, in English, properly formatted.