diff --git a/back/models/notificationSubscription.js b/back/models/notificationSubscription.js
index 674629413..f1b2811fa 100644
--- a/back/models/notificationSubscription.js
+++ b/back/models/notificationSubscription.js
@@ -47,22 +47,16 @@ module.exports = Self => {
     };
 
     async function getUserToModify(notificationId, userFk, models) {
-        if (notificationId != null) {
+        let userToModify = userFk;
+        if (notificationId) {
             const subscription = await models.NotificationSubscription.findById(notificationId);
-            const user = await subscription.userFk;
-            return await models.Worker.findOne({
-                fields: ['id', 'bossFk'],
-                where: {
-                    id: user
-                }
-            });
-        } else {
-            return await models.Worker.findOne({
-                fields: ['id', 'bossFk'],
-                where: {
-                    id: userFk
-                }
-            });
+            userToModify = subscription.userFk;
         }
+        return await models.Worker.findOne({
+            fields: ['id', 'bossFk'],
+            where: {
+                id: userToModify
+            }
+        });
     }
 };
diff --git a/db/changes/230201/00-uniqueKeyNotificationSubscription.sql b/db/changes/230201/00-uniqueKeyNotificationSubscription.sql
new file mode 100644
index 000000000..623ecf770
--- /dev/null
+++ b/db/changes/230201/00-uniqueKeyNotificationSubscription.sql
@@ -0,0 +1,4 @@
+ALTER TABLE
+    `util`.`notificationSubscription`
+ADD
+    CONSTRAINT `notificationSubscription_UN` UNIQUE KEY (`notificationFk`, `userFk`);
\ No newline at end of file