diff --git a/erpnext/selling/doctype/sales_order/sales_order.py b/erpnext/selling/doctype/sales_order/sales_order.py
index c7319e37381c7e10607f1ea816d11bc6d9fc92e5..691edc25b0f55f86811505f2ff1af1d15506761d 100755
--- a/erpnext/selling/doctype/sales_order/sales_order.py
+++ b/erpnext/selling/doctype/sales_order/sales_order.py
@@ -122,7 +122,8 @@ 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(