diff --git a/ordernumbers_woocommerce.php b/ordernumbers_woocommerce.php
index 764a65bc86e2cafb09e5e9c73ecb2f920166dde6..deab2985a00fb9e4957da699e010a83bd564bc14 100644
--- a/ordernumbers_woocommerce.php
+++ b/ordernumbers_woocommerce.php
@@ -241,6 +241,7 @@ class OpenToolsOrdernumbers extends OpenToolsOrdernumbersBasic {
 	}
     
 	public function setupOrderReplacements (&$reps, $order, $nrtype) {
+		$reps["[issuborder]"] = ($order->post->post_parent != 0);
 		$reps["[orderid]"] = $order->id;
 		
 		if ($nrtype != 'ordernumber') {
diff --git a/readme.txt b/readme.txt
index e3c2440019be9938fc01a92c15a55c05ac69ae10..d2866fa966bf624ac567d5771c0135b2b6b1c77f 100644
--- a/readme.txt
+++ b/readme.txt
@@ -79,6 +79,7 @@ The Advanced Ordernumbers for WooCommerce plugin supports some invoicing plugins
 == Changelog ==
 
 = 1.4.0 =
+* Add variables [isSubOrder] to allow admins to use different order number formats for suborders created by the YITH WC Multivendor plugin
 
 = 1.3.9 =
 * Fix issues with the WooCommerce PDF Invoices & Packaging Slips plugin (invoice numbers were created even if disabled and before an invoice was actually generated)