diff --git a/erpnext/regional/report/gstr_1/gstr_1.py b/erpnext/regional/report/gstr_1/gstr_1.py
index 52f0748..9837996 100644
--- a/erpnext/regional/report/gstr_1/gstr_1.py
+++ b/erpnext/regional/report/gstr_1/gstr_1.py
@@ -144,17 +144,10 @@
 		""" % (self.doctype, ', '.join(['%s']*len(self.invoices))), tuple(self.invoices), as_dict=1)
 
 		for d in items:
-			item_details = {}
-			item_details[d.item_code] = d.base_net_amount
-
-			if d.parent in self.invoice_items:
-				parent_dict = self.invoice_items[d.parent]
-				if d.item_code in parent_dict:
-					item_details[d.item_code] += parent_dict[d.item_code]
-				else:
-					item_details.update(parent_dict)
-
-			self.invoice_items[d.parent] = item_details
+			if d.item_code not in self.invoice_items.get(d.parent, {}):
+				self.invoice_items.setdefault(d.parent, {}).setdefault(d.item_code,
+					sum(i.get('base_net_amount', 0) for i in items
+					    if i.item_code == d.item_code and i.parent == d.parent))
 
 	def get_items_based_on_tax_rate(self):
 		self.tax_details = frappe.db.sql("""