diff --git a/erpnext/accounts/doctype/sales_invoice/sales_invoice.py b/erpnext/accounts/doctype/sales_invoice/sales_invoice.py
index 6ab6148..1c4fe3d 100644
--- a/erpnext/accounts/doctype/sales_invoice/sales_invoice.py
+++ b/erpnext/accounts/doctype/sales_invoice/sales_invoice.py
@@ -70,6 +70,7 @@
 		self.clear_unallocated_advances("Sales Invoice Advance", "advances")
 		self.add_remarks()
 		self.validate_write_off_account()
+		self.validate_duplicate_offline_pos_entry()
 		self.validate_account_for_change_amount()
 		self.validate_fixed_asset()
 		self.set_income_account_for_fixed_assets()
@@ -462,6 +463,12 @@
 		if flt(self.write_off_amount) and not self.write_off_account:
 			msgprint(_("Please enter Write Off Account"), raise_exception=1)
 
+	def validate_duplicate_offline_pos_entry(self):
+		if self.is_pos and self.offline_pos_name \
+			and frappe.db.get_value('Sales Invoice',
+			{'offline_pos_name': self.offline_pos_name, 'docstatus': 1}):
+			frappe.throw(_("Duplicate offline pos sales invoice {0}").format(self.offline_pos_name))
+
 	def validate_account_for_change_amount(self):
 		if flt(self.change_amount) and not self.account_for_change_amount:
 			msgprint(_("Please enter Account for Change Amount"), raise_exception=1)