diff --git a/cmd/cart/cart-grain.go b/cmd/cart/cart-grain.go
index 846ba57..a05fdbe 100644
--- a/cmd/cart/cart-grain.go
+++ b/cmd/cart/cart-grain.go
@@ -262,6 +262,7 @@ func (c *CartGrain) UpdateTotals() {
 			value := NewPriceFromIncVat(voucher.Value, 25)
 
 			c.TotalDiscount.Add(*value)
+			c.TotalDiscount.Subtract(*value)
 		}
 	}
 }