diff --git a/erpnext/manufacturing/doctype/work_order/work_order.py b/erpnext/manufacturing/doctype/work_order/work_order.py
index c8c2f9a..2ee848c 100644
--- a/erpnext/manufacturing/doctype/work_order/work_order.py
+++ b/erpnext/manufacturing/doctype/work_order/work_order.py
@@ -1327,7 +1327,7 @@
 		used_serial_nos.extend(get_serial_nos(d.serial_no))
 
 	serial_nos = sorted(list(set(serial_nos) - set(used_serial_nos)))
-	row.serial_no = "\n".join(serial_nos[0 : row.job_card_qty])
+	row.serial_no = "\n".join(serial_nos[0 : cint(row.job_card_qty)])
 
 
 def validate_operation_data(row):