diff --git a/doc/PRE_UPGRADE.d/2023.1~ynh1.md b/doc/PRE_UPGRADE.d/2023.1~ynh1.md
index 626ee01..bb8bb96 100644
--- a/doc/PRE_UPGRADE.d/2023.1~ynh1.md
+++ b/doc/PRE_UPGRADE.d/2023.1~ynh1.md
@@ -1,3 +1,9 @@
+###
+BEWARE! If you did not activate the Mosquitto Broker within this package, please run following command prior to upgrade:
+````yunohost app setting $app mqtt_domain -v your.$app.domain.tld````
+Failure to do so may break the app.
+If you did activate the Mosquitto broker, you can proceed safely.
+
 ###Changelog
 - Move to packaging v2
 - From now on, upgrade of the upstream app will not be handled into the app anymore: a new package version will be published for a new Domoticz version. Internal upgrade is disabled (although you may still use the command line)