diff --git a/services/nginx/app/objects/orders_o.php b/services/nginx/app/objects/orders_o.php
index a039d3dd..ef54330d 100644
--- a/services/nginx/app/objects/orders_o.php
+++ b/services/nginx/app/objects/orders_o.php
@@ -2207,7 +2207,8 @@ class orders_o extends db
         $sql = "SELECT id FROM $this->table
                 WHERE (UPPER(TRIM(reg_1)) = '$reg' OR UPPER(TRIM(reg_2)) = '$reg' OR UPPER(TRIM(reg_3)) = '$reg')
                   AND created_at BETWEEN '$from_date' AND '$to_date'
-                AND deleted_at IS NULL";
+                AND deleted_at IS NULL
+                ORDER BY id ASC";
         $result = $db->query($sql);
         if ($result->num_rows === 0) {
             return []; // No orders found with the registration number in the date range
diff --git a/services/nginx/app/tests/Unit/Orders/OrdersRegistrationDateRangeQueryTest.php b/services/nginx/app/tests/Unit/Orders/OrdersRegistrationDateRangeQueryTest.php
index 3a2ff650..81a29236 100644
--- a/services/nginx/app/tests/Unit/Orders/OrdersRegistrationDateRangeQueryTest.php
+++ b/services/nginx/app/tests/Unit/Orders/OrdersRegistrationDateRangeQueryTest.php
@@ -126,3 +126,26 @@ it('returns early when registration number is blank', function (): void {
         }
     }
 });
+
+it('orders registration-matched orders by id ASC so invoice-collection reassignment is deterministic', function (): void {
+    $dbStub = new OrdersRegistrationDateRangeDbStub();
+    $hadDb = array_key_exists('db', $GLOBALS);
+    $previousDb = $hadDb ? $GLOBALS['db'] : null;
+    $GLOBALS['db'] = $dbStub;
+
+    try {
+        (new orders_o())->getOrdersWithRegistrationNumberInDateRange(
+            'EC21235',
+            '2025-03-01 00:00:00',
+            '2025-04-30 23:59:59'
+        );
+
+        expect($dbStub->lastQuery)->toContain('ORDER BY id ASC');
+    } finally {
+        if ($hadDb) {
+            $GLOBALS['db'] = $previousDb;
+        } else {
+            unset($GLOBALS['db']);
+        }
+    }
+});