diff --git a/src/admin/tables.py b/src/admin/tables.py
index c49221c..d19d2cd 100644
--- a/src/admin/tables.py
+++ b/src/admin/tables.py
@@ -1,3 +1,4 @@
+import sqlite3
 from dataclasses import dataclass
 from typing import Callable
 
@@ -134,9 +135,19 @@ def set_cell(table: str, pk_value, column: str, value) -> None:
         raise ValueError(f"Table inconnue : {table}")
     cfg = TABLES[table]
     coerced = _coerce_value(table, column, value)
-    get_conn().execute(
-        f"UPDATE {table} SET {column} = ? WHERE {cfg.pk} = ?", (coerced, pk_value)
-    )
+    try:
+        cursor = get_conn().execute(
+            f"UPDATE {table} SET {column} = ? WHERE {cfg.pk} = ?", (coerced, pk_value)
+        )
+    except sqlite3.IntegrityError as exc:
+        raise ValueError(
+            f"Écriture refusée pour {column} (contrainte violée) : {value!r}"
+        ) from exc
+    if cursor.rowcount == 0:
+        raise ValueError(
+            f"Ligne introuvable (table={table}, {cfg.pk}={pk_value!r}) — "
+            "probablement supprimée entre-temps."
+        )
 
 
 def find_changed_cell(
diff --git a/tests/admin/test_tables.py b/tests/admin/test_tables.py
index bf55ce7..3ca7382 100644
--- a/tests/admin/test_tables.py
+++ b/tests/admin/test_tables.py
@@ -68,6 +68,28 @@ def test_set_cell_writes_valid_value(users_db_path):
     assert rows[0]["siret"] == "12345678900011"
 
 
+def test_set_cell_raises_valueerror_on_unique_constraint_violation(users_db_path):
+    from src.auth import db as auth_db
+
+    auth_db.init_schema()
+    auth_db.create_user("first@ex.fr", "hash")
+    second_uid = auth_db.create_user("second@ex.fr", "hash")
+
+    with pytest.raises(ValueError):
+        tables.set_cell("users", second_uid, "email", "first@ex.fr")
+
+
+def test_set_cell_raises_valueerror_when_row_missing(users_db_path):
+    from src.auth import db as auth_db
+
+    auth_db.init_schema()
+    uid = auth_db.create_user("a@ex.fr", "hash")
+    auth_db.delete_user(uid)
+
+    with pytest.raises(ValueError):
+        tables.set_cell("users", uid, "email", "new@ex.fr")
+
+
 def test_set_cell_coerces_numeric_type(users_db_path):
     from src.auth import db as auth_db
     from src.subscriptions import db as sub_db