diff --git a/oslo_messaging/tests/test_transport.py b/oslo_messaging/tests/test_transport.py
index 4d37a6a2b..a2c17f9c4 100755
--- a/oslo_messaging/tests/test_transport.py
+++ b/oslo_messaging/tests/test_transport.py
@@ -51,6 +51,13 @@ class _FakeManager(object):
 class GetTransportTestCase(test_utils.BaseTestCase):
 
     scenarios = [
+        ('default',
+         dict(url=None, transport_url=None,
+              control_exchange=None, allowed=None,
+              expect=dict(backend='rabbit',
+                          exchange=None,
+                          url='rabbit:',
+                          allowed=[]))),
         ('transport_url',
          dict(url=None, transport_url='testtransport:',
               control_exchange=None, allowed=None,
@@ -83,8 +90,10 @@ class GetTransportTestCase(test_utils.BaseTestCase):
 
     @mock.patch('oslo_messaging.transport.LOG')
     def test_get_transport(self, fake_logger):
-        self.config(control_exchange=self.control_exchange,
-                    transport_url=self.transport_url)
+        self.messaging_conf.reset()
+        self.config(control_exchange=self.control_exchange)
+        if self.transport_url:
+            self.config(transport_url=self.transport_url)
 
         driver.DriverManager = mock.Mock()
 
diff --git a/oslo_messaging/transport.py b/oslo_messaging/transport.py
index 20ea77896..da4d081b4 100644
--- a/oslo_messaging/transport.py
+++ b/oslo_messaging/transport.py
@@ -42,6 +42,7 @@ LOG = logging.getLogger(__name__)
 
 _transport_opts = [
     cfg.StrOpt('transport_url',
+               default="rabbit://",
                secret=True,
                help='The network address and optional user credentials for '
                     'connecting to the messaging backend, in URL format. The '
@@ -443,8 +444,6 @@ class TransportURL(object):
         if not url:
             conf.register_opts(_transport_opts)
         url = url or conf.transport_url
-        if not url:
-            return cls(conf)
 
         if not isinstance(url, six.string_types):
             raise InvalidTransportURL(url, 'Wrong URL type')