diff --git a/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.json b/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.json
index 9d85cdb..d3e99d5 100755
--- a/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.json
+++ b/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.json
@@ -117,7 +117,7 @@
    "search_index": 1
   }, 
   {
-   "description": "If not applicable please enter: NA", 
+   "description": "", 
    "fieldname": "bill_no", 
    "fieldtype": "Data", 
    "in_filter": 1, 
@@ -758,7 +758,7 @@
  "icon": "icon-file-text", 
  "idx": 1, 
  "is_submittable": 1, 
- "modified": "2014-08-12 05:25:16.261614", 
+ "modified": "2014-08-19 10:36:33.177267", 
  "modified_by": "Administrator", 
  "module": "Accounts", 
  "name": "Purchase Invoice", 
diff --git a/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.py b/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.py
index 68a21d9..2c762f3 100644
--- a/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.py
+++ b/erpnext/accounts/doctype/purchase_invoice/purchase_invoice.py
@@ -89,8 +89,7 @@
 			throw(_("Conversion rate cannot be 0 or 1"))
 
 	def validate_bill_no(self):
-		if self.bill_no and self.bill_no.lower().strip() \
-				not in ['na', 'not applicable', 'none']:
+		if self.bill_no:
 			b_no = frappe.db.sql("""select bill_no, name, ifnull(is_opening,'') from `tabPurchase Invoice`
 				where bill_no = %s and credit_to = %s and docstatus = 1 and name != %s""",
 				(self.bill_no, self.credit_to, self.name))