diff --git a/src/Types/SalesInvoiceStatus.php b/src/Types/SalesInvoiceStatus.php
index 02dc1369..e97f883d 100644
--- a/src/Types/SalesInvoiceStatus.php
+++ b/src/Types/SalesInvoiceStatus.php
@@ -7,15 +7,15 @@ class SalesInvoiceStatus
     /**
      * The sales invoice is in draft status and has not been sent or paid.
      */
-    const DRAFT = 'draft';
+    public const DRAFT = 'draft';
 
     /**
      * The sales invoice has been issued to the customer but has not been paid yet.
      */
-    const ISSUED = 'issued';
+    public const ISSUED = 'issued';
 
     /**
      * The sales invoice has been fully paid.
      */
-    const PAID = 'paid';
+    public const PAID = 'paid';
 }