diff --git a/ewhs/shipments.go b/ewhs/shipments.go
index a4b306c..5ff6a8a 100644
--- a/ewhs/shipments.go
+++ b/ewhs/shipments.go
@@ -46,12 +46,12 @@ type ShipmentLines struct {
 }
 
 type ShipmentListOptions struct {
-	OrderExternalReference string `url:"order_external_reference,omitempty"`
-	From                   string `url:"from,omitempty"`
-	To                     string `url:"to,omitempty"`
-	Limit                  int    `url:"limit,omitempty"`
-	Direction              string `url:"direction,omitempty"`
-	Page                   int    `url:"page,omitempty"`
+	OrderExternalReference []string `url:"order_external_reference,omitempty"`
+	From                   string   `url:"from,omitempty"`
+	To                     string   `url:"to,omitempty"`
+	Limit                  int      `url:"limit,omitempty"`
+	Direction              string   `url:"direction,omitempty"`
+	Page                   int      `url:"page,omitempty"`
 }
 
 func (ss *ShipmentsService) List(ctx context.Context, opts *ShipmentListOptions) (list *[]Shipment, res *Response, err error) {