diff --git a/app/models/departements.py b/app/models/departements.py
index ebe5cc1451..44a963ca0b 100644
--- a/app/models/departements.py
+++ b/app/models/departements.py
@@ -55,6 +55,9 @@ def create_dept(acronym: str, visible=True) -> Departement:
     "Create new departement"
     from app.models import ScoPreference
 
+    existing = Departement.query.filter_by(acronym=acronym).count()
+    if existing:
+        raise ValueError(f"acronyme {acronym} déjà existant")
     departement = Departement(acronym=acronym, visible=visible)
     p1 = ScoPreference(name="DeptName", value=acronym, departement=departement)
     db.session.add(p1)