diff --git a/keystoneclient/v2_0/client.py b/keystoneclient/v2_0/client.py
index b97aa6340..22c6199a5 100644
--- a/keystoneclient/v2_0/client.py
+++ b/keystoneclient/v2_0/client.py
@@ -173,6 +173,8 @@ class Client(httpclient.HTTPClient):
         to a tenant.
         """
         headers = {}
+        if auth_url is None:
+            raise ValueError("Cannot authenticate without a valid auth_url")
         url = auth_url + "/tokens"
         if token:
             headers['X-Auth-Token'] = token
diff --git a/keystoneclient/v3/client.py b/keystoneclient/v3/client.py
index 1f4eebf42..3c60abad1 100644
--- a/keystoneclient/v3/client.py
+++ b/keystoneclient/v3/client.py
@@ -170,6 +170,8 @@ class Client(httpclient.HTTPClient):
                  project_id=None, project_name=None, project_domain_id=None,
                  project_domain_name=None, token=None, trust_id=None):
         headers = {}
+        if auth_url is None:
+            raise ValueError("Cannot authenticate without a valid auth_url")
         url = auth_url + "/auth/tokens"
         body = {'auth': {'identity': {}}}
         ident = body['auth']['identity']
diff --git a/tests/v2_0/test_client.py b/tests/v2_0/test_client.py
index a7a3942f5..3a3505fe1 100644
--- a/tests/v2_0/test_client.py
+++ b/tests/v2_0/test_client.py
@@ -3,6 +3,7 @@ import mock
 
 import requests
 
+from keystoneclient import exceptions
 from keystoneclient.v2_0 import client
 from tests import utils
 from tests.v2_0 import client_fixtures
@@ -90,3 +91,9 @@ class KeystoneClientTest(utils.TestCase):
             self.assertIsNone(new_client.password)
             self.assertEqual(new_client.management_url,
                              'http://admin:35357/v2.0')
+
+    def test_init_err_no_auth_url(self):
+        self.assertRaises(exceptions.AuthorizationFailure,
+                          client.Client,
+                          username='exampleuser',
+                          password='password')
diff --git a/tests/v3/test_client.py b/tests/v3/test_client.py
index c798765c2..e11ce3bde 100644
--- a/tests/v3/test_client.py
+++ b/tests/v3/test_client.py
@@ -3,6 +3,7 @@ import mock
 
 import requests
 
+from keystoneclient import exceptions
 from keystoneclient.v3 import client
 
 from tests import utils
@@ -140,3 +141,9 @@ class KeystoneClientTest(utils.TestCase):
             self.assertEqual(c.auth_ref.trust_id, 'fe0aef')
             self.assertTrue(c.auth_ref.trust_scoped)
             self.assertEquals(c.auth_user_id, '0ca8f6')
+
+    def test_init_err_no_auth_url(self):
+        self.assertRaises(exceptions.AuthorizationFailure,
+                          client.Client,
+                          username='exampleuser',
+                          password='password')