diff --git a/blazar/plugins/instances/instance_plugin.py b/blazar/plugins/instances/instance_plugin.py
index b3fb04c5..9397fab7 100644
--- a/blazar/plugins/instances/instance_plugin.py
+++ b/blazar/plugins/instances/instance_plugin.py
@@ -22,7 +22,6 @@ from oslo_utils.strutils import bool_from_string
 from blazar import context
 from blazar.db import api as db_api
 from blazar.db import utils as db_utils
-from blazar import exceptions
 from blazar.manager import exceptions as mgr_exceptions
 from blazar.plugins import base
 from blazar.plugins import instances as plugin
@@ -315,8 +314,8 @@ class VirtualInstancePlugin(base.BasePlugin, nova.NovaClientWrapper):
         # TODO(masahito) the instance reservation plugin only supports
         # anti-affinity rule in short-term goal.
         if bool_from_string(values['affinity']):
-            raise exceptions.BlazarException('affinity = True is not '
-                                             'supported.')
+            raise mgr_exceptions.MalformedParameter(
+                param='affinity (only affinity = False is supported)')
 
         hosts = self.pickup_hosts(reservation_id, values)
 
@@ -383,8 +382,8 @@ class VirtualInstancePlugin(base.BasePlugin, nova.NovaClientWrapper):
         # TODO(masahito) the instance reservation plugin only supports
         # anti-affinity rule in short-term goal.
         if bool_from_string(new_values.get('affinity', None)):
-            raise exceptions.BlazarException('affinity = True is not '
-                                             'supported.')
+            raise mgr_exceptions.MalformedParameter(
+                param='affinity (only affinity = False is supported)')
 
         reservation = db_api.reservation_get(reservation_id)
         lease = db_api.lease_get(reservation['lease_id'])
diff --git a/blazar/tests/plugins/instances/test_instance_plugin.py b/blazar/tests/plugins/instances/test_instance_plugin.py
index 56c62e02..6d1aaa53 100644
--- a/blazar/tests/plugins/instances/test_instance_plugin.py
+++ b/blazar/tests/plugins/instances/test_instance_plugin.py
@@ -22,7 +22,6 @@ import six
 from blazar import context
 from blazar.db import api as db_api
 from blazar.db import utils as db_utils
-from blazar import exceptions
 from blazar.manager import exceptions as mgr_exceptions
 from blazar.plugins import instances
 from blazar.plugins.instances import instance_plugin
@@ -127,9 +126,9 @@ class TestVirtualInstancePlugin(tests.TestCase):
         inputs = self.get_input_values(2, 4018, 10, 1, True,
                                        '2030-01-01 08:00', '2030-01-01 08:00',
                                        'lease-1', '')
-        self.assertRaises(exceptions.BlazarException, plugin.reserve_resource,
-                          'reservation_id', inputs)
-        self.assertRaises(exceptions.BlazarException,
+        self.assertRaises(mgr_exceptions.MalformedParameter,
+                          plugin.reserve_resource, 'reservation_id', inputs)
+        self.assertRaises(mgr_exceptions.MalformedParameter,
                           plugin.update_reservation, 'reservation_id', inputs)
 
     def test_filter_hosts_by_reservation_with_exclude(self):