diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 70c1c7c8ef..1feae10d55 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -17,6 +17,15 @@ You are welcome to create pull requests on any of those subjects:
 If you want to implement a **new feature**, please [create a corresponding ticket](https://sourceforge.net/p/itop/tickets/new/) for review.   
 If you ever want to begin implementation, do so in a fork, and add a link to the corresponding commits in the ticket.
 
+All **datamodel modification** should be done in an extension. Beware that such change would 
+impact all existing customers, and could prevent them from 
+upgrading!
+Combodo has a long experience of datamodel changes: they are very disruptive! 
+This is why we avoid them in iTop core, especially the changes on existing objects/fields.   
+If you have an idea you're sure would benefit to all of iTop users, you may 
+[create a corresponding ticket](https://sourceforge.net/p/itop/tickets/new/) to submit it, but be warned that there are lots of good 
+reasons to refuse such changes.
+
 ### License
 iTop is distributed under the AGPL-3.0 license (see the [license.txt] file),
 your code must comply with this license.