diff --git a/erpnext/buying/doctype/purchase_order/purchase_order.py b/erpnext/buying/doctype/purchase_order/purchase_order.py
index 43ef287854e..e29e695f48c 100644
--- a/erpnext/buying/doctype/purchase_order/purchase_order.py
+++ b/erpnext/buying/doctype/purchase_order/purchase_order.py
@@ -807,11 +807,19 @@ def get_mapped_purchase_invoice(source_name, target_doc=None, ignore_permissions
 		target.credit_to = get_party_account("Supplier", source.supplier, source.company)
 
 	def update_item(obj, target, source_parent):
-		target.amount = flt(obj.amount) - flt(obj.billed_amt)
-		target.base_amount = target.amount * flt(source_parent.conversion_rate)
-		target.qty = (
-			target.amount / flt(obj.rate) if (flt(obj.rate) and flt(obj.billed_amt)) else flt(obj.qty)
-		)
+		def get_billed_qty(po_item_name):
+			from frappe.query_builder.functions import Sum
+
+			table = frappe.qb.DocType("Purchase Invoice Item")
+			query = (
+				frappe.qb.from_(table)
+				.select(Sum(table.qty).as_("qty"))
+				.where((table.docstatus == 1) & (table.po_detail == po_item_name))
+			)
+			return query.run(pluck="qty")[0] or 0
+
+		billed_qty = flt(get_billed_qty(obj.name))
+		target.qty = flt(obj.qty) - billed_qty
 
 		item = get_item_defaults(target.item_code, source_parent.company)
 		item_group = get_item_group_defaults(target.item_code, source_parent.company)
diff --git a/erpnext/buying/doctype/purchase_order/test_purchase_order.py b/erpnext/buying/doctype/purchase_order/test_purchase_order.py
index c6ee35d6090..206cbc0000e 100644
--- a/erpnext/buying/doctype/purchase_order/test_purchase_order.py
+++ b/erpnext/buying/doctype/purchase_order/test_purchase_order.py
@@ -1286,6 +1286,25 @@ class TestPurchaseOrder(FrappeTestCase):
 		self.assertFalse(po.per_billed)
 		self.assertEqual(po.status, "To Receive and Bill")
 
+	@change_settings("Buying Settings", {"maintain_same_rate": 0})
+	def test_purchase_invoice_creation_with_partial_qty(self):
+		po = create_purchase_order(qty=100, rate=10)
+
+		pi = make_pi_from_po(po.name)
+		pi.items[0].qty = 42
+		pi.items[0].rate = 7.5
+		pi.submit()
+
+		pi = make_pi_from_po(po.name)
+		self.assertEqual(pi.items[0].qty, 58)
+		self.assertEqual(pi.items[0].rate, 10)
+		pi.items[0].qty = 8
+		pi.items[0].rate = 5
+		pi.submit()
+
+		pi = make_pi_from_po(po.name)
+		self.assertEqual(pi.items[0].qty, 50)
+
 
 def create_po_for_sc_testing():
 	from erpnext.controllers.tests.test_subcontracting_controller import (