diff --git a/refstack_client/refstack_client.py b/refstack_client/refstack_client.py
index 4c90eb3..21ffce1 100755
--- a/refstack_client/refstack_client.py
+++ b/refstack_client/refstack_client.py
@@ -523,6 +523,13 @@ class RefstackClient:
         cmd = [wrapper, 'tempest', 'run']
         if not self.args.parallel:
             cmd.append('--serial')
+        # TODO(mkopec) until refstack-client uses tempest tag which contains
+        # the following change https://review.openstack.org/#/c/641349/
+        # let's hardcode concurrency here, when the change is merged, the
+        # value of concurrency will be set as default in tempest so the
+        # following two lines can be deleted
+        cmd.append('--concurrency')
+        cmd.append('0')
         # If a test list was specified, have it take precedence.
         if self.args.test_list:
             self.logger.info("Normalizing test list...")
diff --git a/refstack_client/tests/unit/test_client.py b/refstack_client/tests/unit/test_client.py
index c4f7ff7..e0507aa 100755
--- a/refstack_client/tests/unit/test_client.py
+++ b/refstack_client/tests/unit/test_client.py
@@ -573,7 +573,8 @@ class TestRefstackClient(unittest.TestCase):
 
         mock_popen.assert_called_with(
             ['%s/tools/with_venv.sh' % self.test_path, 'tempest', 'run',
-             '--serial', '--regex', 'tempest.api.compute'],
+             '--serial', '--concurrency', '0', '--regex',
+             'tempest.api.compute'],
             stderr=None
         )
 
@@ -604,7 +605,8 @@ class TestRefstackClient(unittest.TestCase):
         client.test()
         mock_popen.assert_called_with(
             ['%s/tools/with_venv.sh' % self.test_path, 'tempest', 'run',
-             '--serial', '--regex', 'tempest.api.compute'],
+             '--serial', '--concurrency', '0', '--regex',
+             'tempest.api.compute'],
             stderr=None
         )
 
@@ -637,7 +639,8 @@ class TestRefstackClient(unittest.TestCase):
         client.test()
         mock_popen.assert_called_with(
             ['%s/tools/with_venv.sh' % self.test_path, 'tempest', 'run',
-             '--serial', '--regex', 'tempest.api.compute'],
+             '--serial', '--concurrency', '0', '--regex',
+             'tempest.api.compute'],
             stderr=None
         )
 
@@ -678,7 +681,8 @@ class TestRefstackClient(unittest.TestCase):
         mock_whitelist.assert_called_with('test-list.txt')
         mock_popen.assert_called_with(
             ['%s/tools/with_venv.sh' % self.test_path, 'tempest', 'run',
-             '--serial', '--whitelist_file', '/tmp/some-list'],
+             '--serial', '--concurrency', '0', '--whitelist_file',
+             '/tmp/some-list'],
             stderr=None
         )
 
@@ -738,7 +742,8 @@ class TestRefstackClient(unittest.TestCase):
 
         mock_popen.assert_called_with(
             ['%s/tools/with_venv.sh' % self.test_path, 'tempest', 'run',
-             '--serial', '--regex', 'tempest.api.compute'],
+             '--serial', '--concurrency', '0', '--regex',
+             'tempest.api.compute'],
             stderr=None
         )
         # Since '1' is in the next-stream file, we expect the JSON output file