diff --git a/app/models/departements.py b/app/models/departements.py
index 416c5177..6786bf9f 100644
--- a/app/models/departements.py
+++ b/app/models/departements.py
@@ -6,6 +6,7 @@ from typing import Any
 
 from app import db
 from app.models import SHORT_STR_LEN
+from app.scodoc.sco_exceptions import ScoValueError
 
 
 class Departement(db.Model):
@@ -13,7 +14,7 @@ class Departement(db.Model):
 
     id = db.Column(db.Integer, primary_key=True)
     acronym = db.Column(
-        db.String(SHORT_STR_LEN), nullable=False, index=True
+        db.String(SHORT_STR_LEN), nullable=False, index=True, unique=True
     )  # ne change jamais, voir la pref. DeptName
     description = db.Column(db.Text())  # pas utilisé par ScoDoc : voir DeptFullName
     date_creation = db.Column(db.DateTime(timezone=True), server_default=db.func.now())
@@ -60,7 +61,7 @@ def create_dept(acronym: str, visible=True) -> Departement:
 
     existing = Departement.query.filter_by(acronym=acronym).count()
     if existing:
-        raise ValueError(f"acronyme {acronym} déjà existant")
+        raise ScoValueError(f"acronyme {acronym} déjà existant")
     departement = Departement(acronym=acronym, visible=visible)
     p1 = ScoPreference(name="DeptName", value=acronym, departement=departement)
     db.session.add(p1)
diff --git a/migrations/versions/814e8e37d082_unicite_dept_acronym.py b/migrations/versions/814e8e37d082_unicite_dept_acronym.py
new file mode 100644
index 00000000..f035225a
--- /dev/null
+++ b/migrations/versions/814e8e37d082_unicite_dept_acronym.py
@@ -0,0 +1,32 @@
+"""unicite dept_acronym
+
+Revision ID: 814e8e37d082
+Revises: 57179ae34069
+Create Date: 2022-08-04 16:07:59.710487
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = "814e8e37d082"
+down_revision = "57179ae34069"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index("ix_departement_acronym", table_name="departement")
+    op.create_index(
+        op.f("ix_departement_acronym"), "departement", ["acronym"], unique=True
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index(op.f("ix_departement_acronym"), table_name="departement")
+    op.create_index("ix_departement_acronym", "departement", ["acronym"], unique=False)
+    # ### end Alembic commands ###