diff --git a/cmd/cart/mutation_add_voucher.go b/cmd/cart/mutation_add_voucher.go
index 0c24f9a..205438b 100644
--- a/cmd/cart/mutation_add_voucher.go
+++ b/cmd/cart/mutation_add_voucher.go
@@ -2,8 +2,10 @@ package main
 
 import (
 	"fmt"
+	"slices"
 
 	"git.tornberg.me/go-cart-actor/pkg/messages"
+	"git.tornberg.me/go-cart-actor/pkg/voucher"
 )
 
 func (ctx *MutationContext) AddVoucher(g *CartGrain, m *messages.AddVoucher) error {
@@ -11,16 +13,22 @@ func (ctx *MutationContext) AddVoucher(g *CartGrain, m *messages.AddVoucher) err
 		return fmt.Errorf("AddVoucher: nil payload")
 	}
 
-	voucher, err := ctx.VoucherService.GetVoucher(m.Code)
-	if err != nil {
-		return fmt.Errorf("AddVoucher: %w", err)
+	if slices.ContainsFunc(g.Vouchers, func(v *voucher.Voucher) bool {
+		return v.Code == m.Code
+	}) {
+		return fmt.Errorf("voucher already applied")
 	}
 
-	if voucher == nil {
+	voucherData, err := ctx.VoucherService.GetVoucher(m.Code)
+	if err != nil {
+		return fmt.Errorf("cant find voucher: %w", err)
+	}
+
+	if voucherData == nil {
 		return nil
 	}
 
-	g.Vouchers = append(g.Vouchers, voucher)
+	g.Vouchers = append(g.Vouchers, voucherData)
 	g.UpdateTotals()
 	return nil
 }