diff --git a/erpnext/selling/doctype/sales_order/sales_order.py b/erpnext/selling/doctype/sales_order/sales_order.py
index d7cffa3d693035bd112d620fc2d5e522ebb4d888..5a2baf2715a1b28b2b0abb464f85b6fa2ba10482 100755
--- a/erpnext/selling/doctype/sales_order/sales_order.py
+++ b/erpnext/selling/doctype/sales_order/sales_order.py
@@ -124,7 +124,8 @@ class SalesOrder(SellingController):
 					frappe.msgprint(
 						_("Warning: Sales Order {0} already exists against Customer's Purchase Order {1}").format(
 							frappe.bold(so[0][0]), frappe.bold(self.po_no)
-						)
+						),
+						alert=True,
 					)
 				else:
 					frappe.throw(