diff --git a/erpnext/buying/doctype/purchase_order/purchase_order.js b/erpnext/buying/doctype/purchase_order/purchase_order.js
index 25065ab..9f2b971 100644
--- a/erpnext/buying/doctype/purchase_order/purchase_order.js
+++ b/erpnext/buying/doctype/purchase_order/purchase_order.js
@@ -94,7 +94,7 @@
 				if(this.frm.doc.status !== 'Closed' && flt(this.frm.doc.per_received) < 100 && flt(this.frm.doc.per_billed) < 100) {
 					this.frm.add_custom_button(__('Update Items'), () => {
 						erpnext.utils.update_child_items({
-							frm: frm,
+							frm: this.frm,
 							child_docname: "items",
 							child_doctype: "Purchase Order Detail",
 							cannot_add_row: false,