diff --git a/tempest/api/compute/admin/test_quotas.py b/tempest/api/compute/admin/test_quotas.py
index 348666d..9263396 100644
--- a/tempest/api/compute/admin/test_quotas.py
+++ b/tempest/api/compute/admin/test_quotas.py
@@ -13,14 +13,26 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import six
+from testtools import matchers
+
 from tempest.api.compute import base
+from tempest.common import tempest_fixtures as fixtures
 from tempest.common.utils import data_utils
+from tempest.openstack.common import log as logging
 from tempest import test
 
+LOG = logging.getLogger(__name__)
+
 
 class QuotasAdminTestJSON(base.BaseV2ComputeAdminTest):
     force_tenant_isolation = True
 
+    def setUp(self):
+        # NOTE(mriedem): Avoid conflicts with os-quota-class-sets tests.
+        self.useFixture(fixtures.LockFixture('compute_quotas'))
+        super(QuotasAdminTestJSON, self).setUp()
+
     @classmethod
     def setUpClass(cls):
         super(QuotasAdminTestJSON, cls).setUpClass()
@@ -134,3 +146,49 @@
 
 class QuotasAdminTestXML(QuotasAdminTestJSON):
     _interface = 'xml'
+
+
+class QuotaClassesAdminTestJSON(base.BaseV2ComputeAdminTest):
+    """Tests the os-quota-class-sets API to update default quotas.
+    """
+
+    def setUp(self):
+        # All test cases in this class need to externally lock on doing
+        # anything with default quota values.
+        self.useFixture(fixtures.LockFixture('compute_quotas'))
+        super(QuotaClassesAdminTestJSON, self).setUp()
+
+    @classmethod
+    def setUpClass(cls):
+        super(QuotaClassesAdminTestJSON, cls).setUpClass()
+        cls.adm_client = cls.os_adm.quota_classes_client
+
+    def _restore_default_quotas(self, original_defaults):
+        LOG.debug("restoring quota class defaults")
+        resp, body = self.adm_client.update_quota_class_set(
+            'default', **original_defaults)
+        self.assertEqual(200, resp.status)
+
+    @test.attr(type='gate')
+    def test_update_default_quotas(self):
+        LOG.debug("get the current 'default' quota class values")
+        resp, body = self.adm_client.get_quota_class_set('default')
+        self.assertEqual(200, resp.status)
+        self.assertIn('id', body)
+        self.assertEqual('default', body.pop('id'))
+        # restore the defaults when the test is done
+        self.addCleanup(self._restore_default_quotas, body.copy())
+        # increment all of the values for updating the default quota class
+        for quota, default in six.iteritems(body):
+            body[quota] = default + 1
+        LOG.debug("update limits for the default quota class set")
+        resp, update_body = self.adm_client.update_quota_class_set('default',
+                                                                   **body)
+        self.assertEqual(200, resp.status)
+        LOG.debug("assert that the response has all of the changed values")
+        self.assertThat(update_body.items(),
+                        matchers.ContainsAll(body.items()))
+
+
+class QuotaClassesAdminTestXML(QuotaClassesAdminTestJSON):
+    _interface = 'xml'