diff --git a/erpnext/accounts/doctype/pricing_rule/pricing_rule.py b/erpnext/accounts/doctype/pricing_rule/pricing_rule.py
index 83045eae4e..d6b12f1b47 100644
--- a/erpnext/accounts/doctype/pricing_rule/pricing_rule.py
+++ b/erpnext/accounts/doctype/pricing_rule/pricing_rule.py
@@ -131,7 +131,7 @@ def get_serial_no_for_item(args):
 		"name": args.name,
 		"serial_no": args.serial_no
 	})
-	if args.get("parenttype") in ("Sales Invoice", "Delivery Note") and args.stock_qty > 0:
+	if args.get("parenttype") in ("Sales Invoice", "Delivery Note") and flt(args.stock_qty) > 0:
 		item_details.serial_no = get_serial_no(args)
 	return item_details
 
diff --git a/erpnext/accounts/doctype/sales_invoice/sales_invoice.json b/erpnext/accounts/doctype/sales_invoice/sales_invoice.json
index 2bd14472f3..5b52bbba90 100644
--- a/erpnext/accounts/doctype/sales_invoice/sales_invoice.json
+++ b/erpnext/accounts/doctype/sales_invoice/sales_invoice.json
@@ -751,7 +751,7 @@
    "precision": "",
    "print_hide": 0,
    "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": "2018-03-13 15:19:54.711885",
+ "modified": "2018-03-16 15:19:54.711885",
  "modified_by": "Administrator",
  "module": "Accounts",
  "name": "Sales Invoice",