diff --git a/database/migrations/2025_09_22_133425_create_class_characteristics_table.php b/database/migrations/2025_09_22_133425_create_class_characteristics_table.php
index 902b193..c220def 100644
--- a/database/migrations/2025_09_22_133425_create_class_characteristics_table.php
+++ b/database/migrations/2025_09_22_133425_create_class_characteristics_table.php
@@ -178,6 +178,7 @@ return new class extends Migration
                 updated_by							TEXT DEFAULT NULL,
                 deleted_at			                TIMESTAMP,
 
+                UNIQUE (gernr, plant_id),
                 FOREIGN KEY (plant_id)              REFERENCES  plants (id),
                 FOREIGN KEY (machine_id)            REFERENCES  machines (id),
                 FOREIGN KEY (item_id)               REFERENCES  items (id)