diff --git a/contrib/docker/.env.prod.singledomain.template b/contrib/docker/.env.prod.singledomain.template
index 55dd976b..91e73122 100644
--- a/contrib/docker/.env.prod.singledomain.template
+++ b/contrib/docker/.env.prod.singledomain.template
@@ -28,6 +28,9 @@ TRAEFIK_BASICAUTHFILE=/.htpasswd
 # Maximum allowed number of people per "ring" group
 MAX_PER_GROUP=5
 
+# Maximum length allowed for nicknames
+MAX_USERNAME_LENGTH=12
+
 # The URL used by default, in the form: "/_/global/map/url.json" or with active admin backend as "/@/org/world/room"
 START_ROOM_URL=/_/global/maps.workadventu.re/Floor0/floor0.json