diff --git a/erpnext/stock/doctype/serial_no/serial_no.py b/erpnext/stock/doctype/serial_no/serial_no.py
index 9e5963baa3..0408cfe642 100644
--- a/erpnext/stock/doctype/serial_no/serial_no.py
+++ b/erpnext/stock/doctype/serial_no/serial_no.py
@@ -214,9 +214,9 @@ def validate_serial_no(sle, item_det):
 				webnotes.throw(_("Serial Nos do not match with qty") + \
 					(": %s (%s)" % (sle.item_code, sle.actual_qty)), SerialNoQtyError)
 					
-			# if len(serial_nos) != len(set(serial_nos)):
-			# 	webnotes.throw(_("Duplicate Serial No entered against item") + 
-			# 		(": %s" % sle.item_code), SerialNoDuplicateError)
+			if len(serial_nos) != len(set(serial_nos)):
+				webnotes.throw(_("Duplicate Serial No entered against item") + 
+					(": %s" % sle.item_code), SerialNoDuplicateError)
 			
 			for serial_no in serial_nos:
 				if webnotes.conn.exists("Serial No", serial_no):