diff --git a/api-ref/source/servers-actions.inc b/api-ref/source/servers-actions.inc
index 6538e215e1ad..e15d3c06cc83 100644
--- a/api-ref/source/servers-actions.inc
+++ b/api-ref/source/servers-actions.inc
@@ -423,6 +423,29 @@ Reboots a server.
 
 Specify the ``reboot`` action in the request body.
 
+**Preconditions**
+
+The preconditions for rebooting a server depend on the type of reboot.
+
+You can only *SOFT* reboot a server when its status is ``ACTIVE``.
+
+You can only *HARD* reboot a server when its status is one of:
+
+* ``ACTIVE``
+* ``ERROR``
+* ``HARD_REBOOT``
+* ``PAUSED``
+* ``REBOOT``
+* ``SHUTOFF``
+* ``SUSPENDED``
+
+If the server is locked, you must have administrator privileges
+to reboot the server.
+
+**Asynchronous Postconditions**
+
+After you successfully reboot a server, its status changes to ``ACTIVE``.
+
 Normal response codes: 202
 
 Error response codes: unauthorized(401), forbidden(403), itemNotFound(404),
diff --git a/nova/compute/api.py b/nova/compute/api.py
index 3f330b94cc1a..4dbe7bfc6803 100644
--- a/nova/compute/api.py
+++ b/nova/compute/api.py
@@ -3079,15 +3079,7 @@ class API(base.Base):
                           task_state=task_states.ALLOW_REBOOT)
     def _hard_reboot(self, context, instance):
         instance.task_state = task_states.REBOOTING_HARD
-        expected_task_state = [None,
-                               task_states.REBOOTING,
-                               task_states.REBOOT_PENDING,
-                               task_states.REBOOT_STARTED,
-                               task_states.REBOOTING_HARD,
-                               task_states.RESUMING,
-                               task_states.UNPAUSING,
-                               task_states.SUSPENDING]
-        instance.save(expected_task_state = expected_task_state)
+        instance.save(expected_task_state=task_states.ALLOW_REBOOT)
 
         self._record_action_start(context, instance, instance_actions.REBOOT)
 
diff --git a/nova/tests/unit/compute/test_compute.py b/nova/tests/unit/compute/test_compute.py
index 6039a19b328d..af51f6273640 100644
--- a/nova/tests/unit/compute/test_compute.py
+++ b/nova/tests/unit/compute/test_compute.py
@@ -3242,6 +3242,18 @@ class ComputeTestCase(BaseTestCase,
     def test_reboot_fail_running(self):
         self._test_reboot(False, fail_reboot=True, fail_running=True)
 
+    def test_reboot_hard_pausing(self):
+        # We need an actual instance in the database for this test to make
+        # sure that expected_task_state works OK with Instance.save().
+        instance = self._create_fake_instance_obj(
+            params={'task_state': task_states.PAUSING})
+        with mock.patch.object(self.compute_api.compute_rpcapi,
+                               'reboot_instance') as rpc_reboot:
+            self.compute_api.reboot(self.context, instance, 'HARD')
+        rpc_reboot.assert_called_once_with(
+            self.context, instance=instance, block_device_info=None,
+            reboot_type='HARD')
+
     def test_get_instance_block_device_info_source_image(self):
         bdms = block_device_obj.block_device_make_list(self.context,
                 [fake_block_device.FakeDbBlockDeviceDict({
diff --git a/nova/tests/unit/compute/test_compute_api.py b/nova/tests/unit/compute/test_compute_api.py
index 176e6f25b4f9..6cbd16da5e8b 100644
--- a/nova/tests/unit/compute/test_compute_api.py
+++ b/nova/tests/unit/compute/test_compute_api.py
@@ -867,13 +867,7 @@ class _ComputeAPIUnitTestMixIn(object):
 
         expected_task_state = [None]
         if reboot_type == 'HARD':
-            expected_task_state.extend([task_states.REBOOTING,
-                                        task_states.REBOOT_PENDING,
-                                        task_states.REBOOT_STARTED,
-                                        task_states.REBOOTING_HARD,
-                                        task_states.RESUMING,
-                                        task_states.UNPAUSING,
-                                        task_states.SUSPENDING])
+            expected_task_state = task_states.ALLOW_REBOOT
 
         if self.cell_type == 'api':
             rpcapi = self.compute_api.cells_rpcapi
@@ -930,10 +924,6 @@ class _ComputeAPIUnitTestMixIn(object):
         self._test_reboot_type(vm_states.ACTIVE,
                                'HARD', task_state=task_states.RESUMING)
 
-    def test_reboot_hard_pausing(self):
-        self._test_reboot_type(vm_states.ACTIVE,
-                               'HARD', task_state=task_states.PAUSING)
-
     def test_reboot_hard_unpausing(self):
         self._test_reboot_type(vm_states.ACTIVE,
                                'HARD', task_state=task_states.UNPAUSING)