diff --git a/erpnext/controllers/buying_controller.py b/erpnext/controllers/buying_controller.py
index e5012f972b2..dfa8546da0f 100644
--- a/erpnext/controllers/buying_controller.py
+++ b/erpnext/controllers/buying_controller.py
@@ -983,11 +983,11 @@ def get_non_stock_items(purchase_order, fg_item_code):
 def set_serial_nos(raw_material, consumed_serial_nos, qty):
 	consumed_serial_nos_list = []
 
-	if isinstance(consumed_serial_nos, list):
+	if consumed_serial_nos and isinstance(consumed_serial_nos, list):
 		for row in consumed_serial_nos:
 			consumed_serial_nos_list.extend(get_serial_nos(row))
-	else:
-		consumed_serial_nos_list = get_serial_nos(row)
+	elif consumed_serial_nos:
+		consumed_serial_nos_list = get_serial_nos(consumed_serial_nos)
 
 	serial_nos = set(get_serial_nos(raw_material.serial_nos)) - set(consumed_serial_nos_list)