diff --git a/nova/conf/libvirt.py b/nova/conf/libvirt.py
index 4d87ea616a75..abd574bff1d3 100644
--- a/nova/conf/libvirt.py
+++ b/nova/conf/libvirt.py
@@ -721,25 +721,25 @@ http://man7.org/linux/man-pages/man7/random.7.html.
                    ('none', 'A serial number entry is not added to the guest '
                             'domain xml.'),
                    ('os', 'A UUID serial number is generated from the host '
-                          '``/etc/machine-id`` file. This will also affect '
-                          'existing instances on this host once they stop '
-                          'and start again.'),
+                          '``/etc/machine-id`` file.'),
                    ('hardware', 'A UUID for the host hardware as reported by '
                                 'libvirt. This is typically from the host '
                                 'SMBIOS data, unless it has been overridden '
                                 'in ``libvirtd.conf``.'),
                    ('auto', 'Uses the "os" source if possible, else '
                             '"hardware".'),
-                   ('unique', 'Uses instance UUID as the serial number. '
-                              'This will also affect existing instances '
-                              'on this host once they stop and start again.'),
+                   ('unique', 'Uses instance UUID as the serial number.'),
                ),
-               help='The data source used to the populate the host "serial" '
-                    'UUID exposed to guest in the virtual BIOS. All choices '
-                    'except ``unique`` will change the serial when migrating '
-                    'instance to other host. Changing the choice of this '
-                    'option will also affect existing instances on this host '
-                    'once they stopped and started again.'
+               help="""
+The data source used to the populate the host "serial" UUID exposed to guest
+in the virtual BIOS. All choices except ``unique`` will change the serial when
+migrating the instance to another host. Changing the choice of this option will
+also affect existing instances on this host once they are stopped and started
+again. It is recommended to use the default choice (``unique``) since that will
+not change when an instance is migrated. However, if you have a need for
+per-host serials in addition to per-instance serial numbers, then consider
+restricting flavors via host aggregates.
+"""
                ),
     cfg.IntOpt('mem_stats_period_seconds',
                default=10,
diff --git a/nova/tests/unit/virt/libvirt/test_driver.py b/nova/tests/unit/virt/libvirt/test_driver.py
index 12c3e82f86bb..af0a7f8453cf 100644
--- a/nova/tests/unit/virt/libvirt/test_driver.py
+++ b/nova/tests/unit/virt/libvirt/test_driver.py
@@ -17928,7 +17928,7 @@ class TestGuestConfigSysinfoSerialOS(test.NoDBTestCase):
         self.assertEqual(version.version_string_with_package(),
                          cfg.system_version)
         if expected_serial == 'instance_uuid':
-            expected_serial = instance_ref['uuid']
+            expected_serial = instance_ref.uuid
         self.assertEqual(expected_serial,
                          cfg.system_serial)
         self.assertEqual(instance_ref['uuid'],
diff --git a/nova/virt/libvirt/driver.py b/nova/virt/libvirt/driver.py
index 0d18bc5663ad..6d1603373ed0 100644
--- a/nova/virt/libvirt/driver.py
+++ b/nova/virt/libvirt/driver.py
@@ -366,6 +366,9 @@ class LibvirtDriver(driver.ComputeDriver):
         self._volume_api = cinder.API()
         self._image_api = image.API()
 
+        # The default choice for the sysinfo_serial config option is "unique"
+        # which does not have a special function since the value is just the
+        # instance.uuid.
         sysinfo_serial_funcs = {
             'none': lambda: None,
             'hardware': self._get_host_sysinfo_serial_hardware,
diff --git a/releasenotes/notes/per-instance-serial-f2e597cb05d1b09e.yaml b/releasenotes/notes/per-instance-serial-f2e597cb05d1b09e.yaml
index 66ac2f4bab8a..a70ae75cf7d4 100644
--- a/releasenotes/notes/per-instance-serial-f2e597cb05d1b09e.yaml
+++ b/releasenotes/notes/per-instance-serial-f2e597cb05d1b09e.yaml
@@ -3,5 +3,7 @@ upgrade:
   - |
     Added a new ``unique`` choice to the ``[libvirt]/sysinfo_serial``
     configuration which if set will result in the guest serial number being
-    set to ``instance.uuid`` on this host. This is now the default value
-    of ``[libvirt]/sysinfo_serial`` config option.
+    set to ``instance.uuid``. This is now the default value
+    of the ``[libvirt]/sysinfo_serial`` config option and is the recommended
+    choice since it ensures the guest serial is the same even if the instance
+    is migrated between hosts.