diff --git a/fixtures/shippinglines/requested_fulfillment_service_id_invalid.json b/fixtures/shippinglines/requested_fulfillment_service_id_invalid.json
index 3e17ff85..b4fd6362 100644
--- a/fixtures/shippinglines/requested_fulfillment_service_id_invalid.json
+++ b/fixtures/shippinglines/requested_fulfillment_service_id_invalid.json
@@ -1,5 +1,5 @@
 {
-  "id": "some-id",
+  "id": 123456789,
   "code": "INT.TP",
   "price": "4.00",
   "price_set": {
diff --git a/fixtures/shippinglines/requested_fulfillment_service_id_null.json b/fixtures/shippinglines/requested_fulfillment_service_id_null.json
index f5994cbb..73b6f6f9 100644
--- a/fixtures/shippinglines/requested_fulfillment_service_id_null.json
+++ b/fixtures/shippinglines/requested_fulfillment_service_id_null.json
@@ -1,5 +1,5 @@
 {
-  "id": "some-id",
+  "id": 123456789,
   "code": "INT.TP",
   "price": "4.00",
   "price_set": {
diff --git a/fixtures/shippinglines/requested_fulfillment_service_id_number.json b/fixtures/shippinglines/requested_fulfillment_service_id_number.json
index 6d342fc9..cffa6b5c 100644
--- a/fixtures/shippinglines/requested_fulfillment_service_id_number.json
+++ b/fixtures/shippinglines/requested_fulfillment_service_id_number.json
@@ -1,5 +1,5 @@
 {
-  "id": "some-id",
+  "id": 123456789,
   "code": "INT.TP",
   "price": "4.00",
   "price_set": {
diff --git a/fixtures/shippinglines/valid.json b/fixtures/shippinglines/valid.json
index 04f967fd..202258b1 100644
--- a/fixtures/shippinglines/valid.json
+++ b/fixtures/shippinglines/valid.json
@@ -1,5 +1,5 @@
 {
-  "id": "some-id",
+  "id": 123456789,
   "code": "INT.TP",
   "price": "4.00",
   "price_set": {
diff --git a/order.go b/order.go
index 17e9d187..095ed4ad 100644
--- a/order.go
+++ b/order.go
@@ -487,7 +487,7 @@ type PaymentDetails struct {
 }
 
 type ShippingLines struct {
-	Id                            string           `json:"id,omitempty"`
+	Id                            uint64           `json:"id,omitempty"`
 	Title                         string           `json:"title,omitempty"`
 	Price                         *decimal.Decimal `json:"price,omitempty"`
 	PriceSet                      *AmountSet       `json:"price_set,omitempty"`
diff --git a/order_test.go b/order_test.go
index 61a0b8c7..a2d38fd6 100644
--- a/order_test.go
+++ b/order_test.go
@@ -1421,7 +1421,7 @@ func validShippingLines() ShippingLines {
 	tl2Rate := decimal.New(5, -2)
 
 	return ShippingLines{
-		Id:    "some-id",
+		Id:    123456789,
 		Title: "Small Packet International Air",
 		Price: &price,
 		PriceSet: &AmountSet{