diff --git a/modules/purchase/purchase.py b/modules/purchase/purchase.py
index 9215127..c197555 100755
--- a/modules/purchase/purchase.py
+++ b/modules/purchase/purchase.py
@@ -1685,7 +1685,7 @@ class Line(sequence_ordered(), ModelSQL, ModelView):
 
     @fields.depends(
         'type', 'quantity', 'unit_price',
-        'purchase', '_parent_purchase.currency')
+        'purchase', '_parent_purchase.currency','premium')
     def on_change_with_amount(self):
         if (self.type == 'line'
                 and self.quantity is not None