diff --git a/netbox/virtualization/migrations/0041_convert_disk_size.py b/netbox/virtualization/migrations/0041_convert_disk_size.py
index 755fec27e..dd3f4c0ca 100644
--- a/netbox/virtualization/migrations/0041_convert_disk_size.py
+++ b/netbox/virtualization/migrations/0041_convert_disk_size.py
@@ -1,7 +1,7 @@
 # Generated by Django 5.0.7 on 2024-07-31 05:40
 
 from django.db import migrations
-from django.db.models import F
+from django.db.models import F, Sum
 
 
 def convert_disk_size(apps, schema_editor):
@@ -13,7 +13,7 @@ def convert_disk_size(apps, schema_editor):
     VirtualMachine = apps.get_model('virtualization', 'VirtualMachine')
     vms = VirtualMachine.objects.filter(id__in=id_list)
     for vm in vms:
-        vm.disk = self.virtualdisks.aggregate(Sum('size', default=0))['size__sum']
+        vm.disk = vm.virtualdisks.aggregate(Sum('size', default=0))['size__sum']
         vm.save()