diff --git a/erpnext/accounts/report/purchase_register/purchase_register.py b/erpnext/accounts/report/purchase_register/purchase_register.py
index 44410a26bac..717546b0f93 100644
--- a/erpnext/accounts/report/purchase_register/purchase_register.py
+++ b/erpnext/accounts/report/purchase_register/purchase_register.py
@@ -309,17 +309,22 @@ def get_account_columns(invoice_list, include_payments):
 	unrealized_profit_loss_account_columns = []
 
 	if invoice_list:
-		expense_accounts = frappe.get_all(
-			"Purchase Invoice Item",
-			filters={
-				"docstatus": 1,
-				"expense_account": ["is", "set"],
-				"parenttype": "Purchase Invoice",
-				"parent": ["in", [inv.name for inv in invoice_list]],
-			},
-			pluck="expense_account",
-			distinct=True,
-			order_by="expense_account",
+		# frappe drops ORDER BY for distinct queries on postgres (db_query), so sort in python with
+		# casefold to keep the generated account-column order deterministic and identical on both
+		# backends, matching MariaDB's case-insensitive collation (the original ORDER BY).
+		expense_accounts = sorted(
+			frappe.get_all(
+				"Purchase Invoice Item",
+				filters={
+					"docstatus": 1,
+					"expense_account": ["is", "set"],
+					"parenttype": "Purchase Invoice",
+					"parent": ["in", [inv.name for inv in invoice_list]],
+				},
+				pluck="expense_account",
+				distinct=True,
+			),
+			key=str.casefold,
 		)
 
 		purchase_taxes_query = get_taxes_query(invoice_list, "Purchase Taxes and Charges", "Purchase Invoice")
@@ -331,16 +336,18 @@ def get_account_columns(invoice_list, include_payments):
 			advance_tax_accounts = advance_taxes_query.run(as_dict=True, pluck="account_head")
 			tax_accounts = set(tax_accounts + advance_tax_accounts)
 
-		unrealized_profit_loss_accounts = frappe.get_all(
-			"Purchase Invoice",
-			filters={
-				"docstatus": 1,
-				"name": ["in", [inv.name for inv in invoice_list]],
-				"unrealized_profit_loss_account": ["is", "set"],
-			},
-			pluck="unrealized_profit_loss_account",
-			distinct=True,
-			order_by="unrealized_profit_loss_account",
+		unrealized_profit_loss_accounts = sorted(
+			frappe.get_all(
+				"Purchase Invoice",
+				filters={
+					"docstatus": 1,
+					"name": ["in", [inv.name for inv in invoice_list]],
+					"unrealized_profit_loss_account": ["is", "set"],
+				},
+				pluck="unrealized_profit_loss_account",
+				distinct=True,
+			),
+			key=str.casefold,
 		)
 
 	for account in expense_accounts:
diff --git a/erpnext/accounts/report/purchase_register/test_purchase_register.py b/erpnext/accounts/report/purchase_register/test_purchase_register.py
index 9e0e2002f60..f72035496a7 100644
--- a/erpnext/accounts/report/purchase_register/test_purchase_register.py
+++ b/erpnext/accounts/report/purchase_register/test_purchase_register.py
@@ -24,6 +24,29 @@ class TestPurchaseRegister(ERPNextTestSuite):
 		self.assertEqual(first_row.total_tax, 100)
 		self.assertEqual(first_row.grand_total, 1100)
 
+	def test_expense_account_columns_sorted_case_insensitively(self):
+		# The dynamic expense-account columns must follow MariaDB's case-insensitive collation order and
+		# be identical on both engines. frappe drops ORDER BY for distinct queries on postgres, so the
+		# report sorts in python with casefold; plain sorted() would be case-sensitive ("ZZZ" < "aaa").
+		from erpnext.accounts.doctype.account.test_account import create_account
+		from erpnext.accounts.doctype.purchase_invoice.test_purchase_invoice import make_purchase_invoice
+
+		company = "_Test Company"
+		lower = create_account(
+			account_name="aaa Test Expense", parent_account="Expenses - _TC", company=company
+		)
+		upper = create_account(
+			account_name="ZZZ Test Expense", parent_account="Expenses - _TC", company=company
+		)
+		for account in (upper, lower):  # submit in non-casefold order
+			make_purchase_invoice(company=company, expense_account=account)
+
+		filters = frappe._dict(company=company, from_date=add_months(today(), -1), to_date=today())
+		columns = execute(filters)[0]
+		labels = [col["label"] for col in columns if col.get("label") in (lower, upper)]
+
+		self.assertEqual(labels, sorted([lower, upper], key=str.casefold))
+
 	def test_purchase_register_ignores_tax_rows_from_other_doctype(self):
 		filters = frappe._dict(company="_Test Company 6", from_date=add_months(today(), -1), to_date=today())