diff --git a/erpnext/manufacturing/report/production_planning_report/production_planning_report.py b/erpnext/manufacturing/report/production_planning_report/production_planning_report.py
index 7130c2c63ea..4ce607b11a1 100644
--- a/erpnext/manufacturing/report/production_planning_report/production_planning_report.py
+++ b/erpnext/manufacturing/report/production_planning_report/production_planning_report.py
@@ -233,7 +233,10 @@ class ProductionPlanReport:
 			fields=[
 				"item_code",
 				{"MIN": "schedule_date", "as": "arrival_date"},
-				"qty as arrival_qty",
+				# qty is not in the GROUP BY, so it must be aggregated to be valid on postgres; sum the
+				# on-order qty per item+warehouse (the meaningful "arriving" figure) instead of MariaDB's
+				# arbitrary single-row pick.
+				{"SUM": "qty", "as": "arrival_qty"},
 				"warehouse",
 			],
 			filters={
diff --git a/erpnext/manufacturing/report/production_planning_report/test_production_planning_report.py b/erpnext/manufacturing/report/production_planning_report/test_production_planning_report.py
new file mode 100644
index 00000000000..10a427aa38e
--- /dev/null
+++ b/erpnext/manufacturing/report/production_planning_report/test_production_planning_report.py
@@ -0,0 +1,47 @@
+# Copyright (c) 2025, Frappe Technologies Pvt. Ltd. and Contributors
+# See license.txt
+
+from erpnext.tests.utils import ERPNextTestSuite
+
+
+class TestProductionPlanningReport(ERPNextTestSuite):
+	def test_report_runs_and_sums_on_order_qty(self):
+		# get_purchase_details groups Purchase Order Item by (item_code, warehouse) while summing qty;
+		# this exercises that GROUP BY on both engines (loose on MariaDB, must be aggregated on Postgres).
+		from erpnext.buying.doctype.purchase_order.test_purchase_order import create_purchase_order
+		from erpnext.manufacturing.doctype.work_order.test_work_order import make_wo_order_test_record
+		from erpnext.manufacturing.report.production_planning_report.production_planning_report import execute
+
+		wh = "_Test Warehouse - _TC"
+		wo = make_wo_order_test_record(production_item="_Test FG Item", qty=2, source_warehouse=wh)
+		self.addCleanup(self._cancel_and_delete, "Work Order", wo.name)
+
+		rm = wo.required_items[0].item_code
+		for qty in (3, 4):
+			po = create_purchase_order(item_code=rm, warehouse=wh, qty=qty, rate=10)
+			self.addCleanup(self._cancel_and_delete, "Purchase Order", po.name)
+
+		filters = {
+			"company": "_Test Company",
+			"based_on": "Work Order",
+			"docnames": [wo.name],
+			"raw_material_warehouse": wh,
+		}
+		columns, data = execute(filters)
+
+		self.assertTrue(columns)
+		rm_rows = [d for d in data if d.get("item_code") == rm and d.get("arrival_qty")]
+		self.assertTrue(rm_rows)
+		# both on-order PO lines (3 + 4) are summed, not arbitrary-picked
+		self.assertEqual(rm_rows[0]["arrival_qty"], 7)
+
+	@staticmethod
+	def _cancel_and_delete(doctype, name):
+		import frappe
+
+		if not frappe.db.exists(doctype, name):
+			return
+		doc = frappe.get_doc(doctype, name)
+		if doc.docstatus == 1:
+			doc.cancel()
+		frappe.delete_doc(doctype, name, force=1)