diff --git a/erpnext/regional/doctype/gstr_3b_report/gstr_3b_report.py b/erpnext/regional/doctype/gstr_3b_report/gstr_3b_report.py
index 6415204..6a61ae2 100644
--- a/erpnext/regional/doctype/gstr_3b_report/gstr_3b_report.py
+++ b/erpnext/regional/doctype/gstr_3b_report/gstr_3b_report.py
@@ -214,9 +214,8 @@
 
 			for d in 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('taxable_value', 0) or i.get('base_net_amount', 0)) for i in item_details
-							if i.item_code == d.item_code and i.parent == d.parent))
+					self.invoice_items.setdefault(d.parent, {}).setdefault(d.item_code, 0.0)
+					self.invoice_items[d.parent][d.item_code] += d.get('taxable_value', 0) or d.get('base_net_amount', 0)
 
 				if d.is_nil_exempt and d.item_code not in self.is_nil_exempt:
 					self.is_nil_exempt.append(d.item_code)
diff --git a/erpnext/regional/report/gstr_1/gstr_1.py b/erpnext/regional/report/gstr_1/gstr_1.py
index cfcb8c3..b81fa81 100644
--- a/erpnext/regional/report/gstr_1/gstr_1.py
+++ b/erpnext/regional/report/gstr_1/gstr_1.py
@@ -217,9 +217,8 @@
 
 		for d in items:
 			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('taxable_value', 0) or i.get('base_net_amount', 0)) for i in items
-						if i.item_code == d.item_code and i.parent == d.parent))
+				self.invoice_items.setdefault(d.parent, {}).setdefault(d.item_code, 0.0)
+				self.invoice_items[d.parent][d.item_code] += d.get('taxable_value', 0) or d.get('base_net_amount', 0)
 
 				item_tax_rate = {}