diff --git a/erpnext/accounts/doctype/sales_invoice/sales_invoice.json b/erpnext/accounts/doctype/sales_invoice/sales_invoice.json
index e00f075f856..2bd14472f30 100644
--- a/erpnext/accounts/doctype/sales_invoice/sales_invoice.json
+++ b/erpnext/accounts/doctype/sales_invoice/sales_invoice.json
@@ -687,12 +687,12 @@
    "in_standard_filter": 0,
    "label": "Customer's Purchase Order",
    "length": 0,
-   "no_copy": 0,
+   "no_copy": 1,
    "permlevel": 0,
    "precision": "",
    "print_hide": 1,
    "print_hide_if_no_value": 0,
-   "read_only": 1,
+   "read_only": 0,
    "remember_last_selected_value": 0,
    "report_hide": 0,
    "reqd": 0,
@@ -4683,7 +4683,7 @@
  "istable": 0,
  "max_attachments": 0,
  "menu_index": 0,
- "modified": "2018-01-12 15:19:54.711885",
+ "modified": "2018-03-13 15:19:54.711885",
  "modified_by": "Administrator",
  "module": "Accounts",
  "name": "Sales Invoice",
diff --git a/erpnext/controllers/selling_controller.py b/erpnext/controllers/selling_controller.py
index 6b18b826bd5..ad32ab59581 100644
--- a/erpnext/controllers/selling_controller.py
+++ b/erpnext/controllers/selling_controller.py
@@ -38,6 +38,7 @@ class SellingController(StockController):
 		self.validate_max_discount()
 		self.validate_selling_price()
 		self.set_qty_as_per_stock_uom()
+		self.set_po_nos()
 		check_active_sales_items(self)
 
 	def set_missing_values(self, for_validate=False):
@@ -326,9 +327,16 @@ class SellingController(StockController):
 							"actual_qty": -1*flt(d.qty),
 							"incoming_rate": return_rate
 						}))
-
 		self.make_sl_entries(sl_entries)
 
+	def set_po_nos(self):
+		if self.doctype in ("Delivery Note", "Sales Invoice"):
+			ref_fieldname = "against_sales_order" if self.doctype == "Delivery Note" else "sales_order"
+			sales_orders = list(set([d.get(ref_fieldname) for d in self.items]))
+			if sales_orders:
+				po_nos = frappe.get_all('Sales Order', 'po_no', filters = {'name': ('in', sales_orders)})
+				self.po_no = ', '.join(list(set([d.po_no for d in po_nos if d.po_no])))
+
 def check_active_sales_items(obj):
 	for d in obj.get("items"):
 		if d.item_code:
diff --git a/erpnext/selling/doctype/sales_order/sales_order.py b/erpnext/selling/doctype/sales_order/sales_order.py
index 2f413072d63..9e309397a29 100644
--- a/erpnext/selling/doctype/sales_order/sales_order.py
+++ b/erpnext/selling/doctype/sales_order/sales_order.py
@@ -5,7 +5,7 @@ from __future__ import unicode_literals
 import frappe
 import json
 import frappe.utils
-from frappe.utils import cstr, flt, getdate, comma_and, cint, nowdate, add_days
+from frappe.utils import cstr, flt, getdate, comma_and, cint
 from frappe import _
 from frappe.model.utils import get_fetch_values
 from frappe.model.mapper import get_mapped_doc
@@ -477,13 +477,9 @@ def make_project(source_name, target_doc=None):
 @frappe.whitelist()
 def make_delivery_note(source_name, target_doc=None):
 	def set_missing_values(source, target):
-		so = [d.against_sales_order for d in target.items]
-		if so:
-			po_no_list = frappe.get_all('Sales Order', 'po_no', filters = {'name': ('in', so)})
-			target.po_no = ', '.join(d.po_no for d in po_no_list if d.po_no)
-
 		target.ignore_pricing_rule = 1
 		target.run_method("set_missing_values")
+		target.run_method("set_po_nos")
 		target.run_method("calculate_taxes_and_totals")
 
 		# set company address
@@ -544,6 +540,7 @@ def make_sales_invoice(source_name, target_doc=None, ignore_permissions=False):
 		target.ignore_pricing_rule = 1
 		target.flags.ignore_permissions = True
 		target.run_method("set_missing_values")
+		target.run_method("set_po_nos")
 		target.run_method("calculate_taxes_and_totals")
 
 		# set company address
diff --git a/erpnext/stock/doctype/delivery_note/delivery_note.json b/erpnext/stock/doctype/delivery_note/delivery_note.json
index f126b581d9b..5c7d116f8d2 100644
--- a/erpnext/stock/doctype/delivery_note/delivery_note.json
+++ b/erpnext/stock/doctype/delivery_note/delivery_note.json
@@ -508,14 +508,14 @@
    "in_standard_filter": 0, 
    "label": "Customer's Purchase Order No", 
    "length": 0, 
-   "no_copy": 0, 
+   "no_copy": 1, 
    "oldfieldname": "po_no", 
    "oldfieldtype": "Data", 
    "permlevel": 0, 
    "print_hide": 1, 
    "print_hide_if_no_value": 0, 
    "print_width": "100px", 
-   "read_only": 1, 
+   "read_only": 0, 
    "remember_last_selected_value": 0, 
    "report_hide": 0, 
    "reqd": 0, 
@@ -3701,7 +3701,7 @@
  "istable": 0, 
  "max_attachments": 0, 
  "menu_index": 0, 
- "modified": "2018-01-12 15:27:44.471335", 
+ "modified": "2018-03-13 15:35:02.234116", 
  "modified_by": "Administrator", 
  "module": "Stock", 
  "name": "Delivery Note", 
diff --git a/erpnext/stock/doctype/delivery_note/delivery_note.py b/erpnext/stock/doctype/delivery_note/delivery_note.py
index 65f384f6d90..07c105c7a1f 100644
--- a/erpnext/stock/doctype/delivery_note/delivery_note.py
+++ b/erpnext/stock/doctype/delivery_note/delivery_note.py
@@ -387,6 +387,7 @@ def make_sales_invoice(source_name, target_doc=None):
 		target.is_pos = 0
 		target.ignore_pricing_rule = 1
 		target.run_method("set_missing_values")
+		target.run_method("set_po_nos")
 
 		if len(target.get("items")) == 0:
 			frappe.throw(_("All these items have already been invoiced"))