diff --git a/ironic/drivers/modules/redfish/management.py b/ironic/drivers/modules/redfish/management.py
index 04e3d96b0c..ba05179e99 100644
--- a/ironic/drivers/modules/redfish/management.py
+++ b/ironic/drivers/modules/redfish/management.py
@@ -303,6 +303,19 @@ class RedfishManagement(base.ManagementInterface):
                          {'node': task.node.uuid, 'mode': mode,
                           'error': e})
             LOG.error(error_msg)
+
+            # NOTE(sbaker): Some systems such as HPE Gen9 do not support
+            # getting or setting the boot mode. When setting failed and the
+            # mode attribute is missing from the boot field, raising
+            # UnsupportedDriverExtension will allow the deploy to continue.
+            if system.boot.get('mode') is None:
+                LOG.info(_('Attempt to set boot mode on node %(node)s '
+                           'failed to set boot mode as the node does not '
+                           'appear to support overriding the boot mode. '
+                           'Possibly partial Redfish implementation?'),
+                         {'node': task.node.uuid})
+                raise exception.UnsupportedDriverExtension(
+                    driver=task.node.driver, extension='set_boot_mode')
             raise exception.RedfishError(error=error_msg)
 
     def get_boot_mode(self, task):
diff --git a/ironic/tests/unit/drivers/modules/redfish/test_management.py b/ironic/tests/unit/drivers/modules/redfish/test_management.py
index 5bc5aaf418..3a48ce76d2 100644
--- a/ironic/tests/unit/drivers/modules/redfish/test_management.py
+++ b/ironic/tests/unit/drivers/modules/redfish/test_management.py
@@ -336,6 +336,12 @@ class RedfishManagementTestCase(db_base.DbTestCase):
 
     @mock.patch.object(redfish_utils, 'get_system', autospec=True)
     def test_set_boot_mode(self, mock_get_system):
+        boot_attribute = {
+            'target': sushy.BOOT_SOURCE_TARGET_PXE,
+            'enabled': sushy.BOOT_SOURCE_ENABLED_CONTINUOUS,
+            'mode': sushy.BOOT_SOURCE_MODE_BIOS,
+        }
+        fake_system = mock.Mock(boot=boot_attribute)
         fake_system = mock.Mock()
         mock_get_system.return_value = fake_system
         with task_manager.acquire(self.context, self.node.uuid,
@@ -383,7 +389,12 @@ class RedfishManagementTestCase(db_base.DbTestCase):
     @mock.patch.object(sushy, 'Sushy', autospec=True)
     @mock.patch.object(redfish_utils, 'get_system', autospec=True)
     def test_set_boot_mode_fail(self, mock_get_system, mock_sushy):
-        fake_system = mock.Mock()
+        boot_attribute = {
+            'target': sushy.BOOT_SOURCE_TARGET_PXE,
+            'enabled': sushy.BOOT_SOURCE_ENABLED_CONTINUOUS,
+            'mode': sushy.BOOT_SOURCE_MODE_BIOS,
+        }
+        fake_system = mock.Mock(boot=boot_attribute)
         fake_system.set_system_boot_options.side_effect = (
             sushy.exceptions.SushyError)
         mock_get_system.return_value = fake_system
@@ -396,6 +407,27 @@ class RedfishManagementTestCase(db_base.DbTestCase):
                 mode=boot_modes.UEFI)
             mock_get_system.assert_called_once_with(task.node)
 
+    @mock.patch.object(sushy, 'Sushy', autospec=True)
+    @mock.patch.object(redfish_utils, 'get_system', autospec=True)
+    def test_set_boot_mode_unsupported(self, mock_get_system, mock_sushy):
+        boot_attribute = {
+            'target': sushy.BOOT_SOURCE_TARGET_PXE,
+            'enabled': sushy.BOOT_SOURCE_ENABLED_CONTINUOUS,
+        }
+        fake_system = mock.Mock(boot=boot_attribute)
+        error = sushy.exceptions.BadRequestError('PATCH', '/', mock.Mock())
+        fake_system.set_system_boot_options.side_effect = error
+        mock_get_system.return_value = fake_system
+        with task_manager.acquire(self.context, self.node.uuid,
+                                  shared=False) as task:
+            self.assertRaisesRegex(
+                exception.UnsupportedDriverExtension,
+                'does not support set_boot_mode',
+                task.driver.management.set_boot_mode, task, boot_modes.UEFI)
+            fake_system.set_system_boot_options.assert_called_once_with(
+                mode=boot_modes.UEFI)
+            mock_get_system.assert_called_once_with(task.node)
+
     @mock.patch.object(redfish_utils, 'get_system', autospec=True)
     def test_get_boot_mode(self, mock_get_system):
         boot_attribute = {
diff --git a/ironic/tests/unit/drivers/third_party_driver_mocks.py b/ironic/tests/unit/drivers/third_party_driver_mocks.py
index ab1f493bb7..ca5199a79c 100644
--- a/ironic/tests/unit/drivers/third_party_driver_mocks.py
+++ b/ironic/tests/unit/drivers/third_party_driver_mocks.py
@@ -228,6 +228,8 @@ if not sushy:
         type('ResourceNotFoundError', (sushy.exceptions.SushyError,), {}))
     sushy.exceptions.MissingAttributeError = (
         type('MissingAttributeError', (sushy.exceptions.SushyError,), {}))
+    sushy.exceptions.BadRequestError = (
+        type('BadRequestError', (sushy.exceptions.SushyError,), {}))
     sushy.auth = mock.MagicMock(spec_set=mock_specs.SUSHY_AUTH_SPEC)
     sys.modules['sushy.auth'] = sushy.auth
 
diff --git a/releasenotes/notes/redfish-boot-mode-override-not-present-handling-92e7263617e467c4.yaml b/releasenotes/notes/redfish-boot-mode-override-not-present-handling-92e7263617e467c4.yaml
new file mode 100644
index 0000000000..79f20e4390
--- /dev/null
+++ b/releasenotes/notes/redfish-boot-mode-override-not-present-handling-92e7263617e467c4.yaml
@@ -0,0 +1,9 @@
+---
+fixes:
+  - |
+    Adds handling of Redfish BMC's which lack a ``BootSourceOverrideMode``
+    flag, such that it is no longer a fatal error for a deployment if the BMC
+    does not support this field. This most common on BMCs which feature only
+    a partial implementation of the ``ComputerSystem`` resource ``boot``,
+    but may also be observable on some older generations of BMCs which
+    recieved updates to have partial Redfish support.