diff --git a/erpnext/manufacturing/doctype/master_production_schedule/master_production_schedule.py b/erpnext/manufacturing/doctype/master_production_schedule/master_production_schedule.py
index 9698bd8eb49..d541c5e19ea 100644
--- a/erpnext/manufacturing/doctype/master_production_schedule/master_production_schedule.py
+++ b/erpnext/manufacturing/doctype/master_production_schedule/master_production_schedule.py
@@ -292,7 +292,7 @@ class MasterProductionSchedule(Document):
 		return item_wise_data
 
 	def add_mps_data(self, data):
-		data = frappe._dict(sorted(data.items(), key=lambda x: x[0][1]))
+		data = frappe._dict(sorted(data.items(), key=lambda x: x[0][1] or ""))
 
 		for key in data:
 			row = data[key]