diff --git a/wiki_groups/views.py b/wiki_groups/views.py
index e2055f1..b43e92f 100644
--- a/wiki_groups/views.py
+++ b/wiki_groups/views.py
@@ -174,7 +174,13 @@ class AddGroupView(WikiGroupMixin, BaseFormView):
         group = self.object
 
         if group.group_in_cycle(list(group.includes_groups.all()) + [subgroup]):
-            form.add_error("group", "Ajout impossible sous peine de créer un cycle")
+            form.add_error(
+                "group",
+                (
+                    "Ajout impossible sous peine de créer un cycle "
+                    f"({group} est inclus dans {subgroup})"
+                ),
+            )
             return self.form_invalid(form)
 
         group.includes_groups.add(subgroup)