diff --git a/app/auth/models.py b/app/auth/models.py
index 329bc3868..d3548cb13 100644
--- a/app/auth/models.py
+++ b/app/auth/models.py
@@ -270,6 +270,8 @@ class User(UserMixin, db.Model):
         """Add a role to this user.
         :param role: Role to add.
         """
+        if not isinstance(role, Role):
+            raise ScoValueError("add_role: rôle invalide")
         self.user_roles.append(UserRole(user=self, role=role, dept=dept))
 
     def add_roles(self, roles, dept):
@@ -281,7 +283,9 @@ class User(UserMixin, db.Model):
 
     def set_roles(self, roles, dept):
         "set roles in the given dept"
-        self.user_roles = [UserRole(user=self, role=r, dept=dept) for r in roles]
+        self.user_roles = [
+            UserRole(user=self, role=r, dept=dept) for r in roles if isinstance(r, Role)
+        ]
 
     def get_roles(self):
         "iterator on my roles"
@@ -292,7 +296,11 @@ class User(UserMixin, db.Model):
         """string repr. of user's roles (with depts)
         e.g. "Ens_RT, Ens_Info, Secr_CJ"
         """
-        return ",".join(f"{r.role.name or ''}_{r.dept or ''}" for r in self.user_roles)
+        return ",".join(
+            f"{r.role.name or ''}_{r.dept or ''}"
+            for r in self.user_roles
+            if r is not None
+        )
 
     def is_administrator(self):
         "True if i'm an active SuperAdmin"