diff --git a/keystoneclient/auth/identity/v2.py b/keystoneclient/auth/identity/v2.py
index 174f89937..1668a825f 100644
--- a/keystoneclient/auth/identity/v2.py
+++ b/keystoneclient/auth/identity/v2.py
@@ -95,11 +95,14 @@ class Auth(base.BaseIdentityPlugin):
         """
 
 
+_NOT_PASSED = object()
+
+
 class Password(Auth):
 
     @utils.positional(4)
-    def __init__(self, auth_url, username=None, password=None, user_id=None,
-                 **kwargs):
+    def __init__(self, auth_url, username=_NOT_PASSED, password=None,
+                 user_id=_NOT_PASSED, **kwargs):
         """A plugin for authenticating with a username and password.
 
         A username or user_id must be provided.
@@ -113,10 +116,15 @@ class Password(Auth):
         """
         super(Password, self).__init__(auth_url, **kwargs)
 
-        if not (user_id or username):
+        if username is _NOT_PASSED and user_id is _NOT_PASSED:
             msg = 'You need to specify either a username or user_id'
             raise TypeError(msg)
 
+        if username is _NOT_PASSED:
+            username = None
+        if user_id is _NOT_PASSED:
+            user_id = None
+
         self.user_id = user_id
         self.username = username
         self.password = password
diff --git a/keystoneclient/tests/auth/test_identity_v2.py b/keystoneclient/tests/auth/test_identity_v2.py
index 52e178bd0..d832f1403 100644
--- a/keystoneclient/tests/auth/test_identity_v2.py
+++ b/keystoneclient/tests/auth/test_identity_v2.py
@@ -100,6 +100,7 @@ class V2IdentityPlugin(utils.TestCase):
         self.stub_auth(json=self.TEST_RESPONSE_DICT)
         a = v2.Password(self.TEST_URL, username=self.TEST_USER,
                         password=self.TEST_PASS)
+        self.assertIsNone(a.user_id)
         s = session.Session(a)
         s.get_token()
 
@@ -114,6 +115,7 @@ class V2IdentityPlugin(utils.TestCase):
         self.stub_auth(json=self.TEST_RESPONSE_DICT)
         a = v2.Password(self.TEST_URL, user_id=self.TEST_USER,
                         password=self.TEST_PASS)
+        self.assertIsNone(a.username)
         s = session.Session(a)
         s.get_token()
 
@@ -128,6 +130,7 @@ class V2IdentityPlugin(utils.TestCase):
         self.stub_auth(json=self.TEST_RESPONSE_DICT)
         a = v2.Password(self.TEST_URL, username=self.TEST_USER,
                         password=self.TEST_PASS, tenant_id=self.TEST_TENANT_ID)
+        self.assertIsNone(a.user_id)
         s = session.Session(a)
         s.get_token()
 
@@ -141,6 +144,7 @@ class V2IdentityPlugin(utils.TestCase):
         self.stub_auth(json=self.TEST_RESPONSE_DICT)
         a = v2.Password(self.TEST_URL, user_id=self.TEST_USER,
                         password=self.TEST_PASS, tenant_id=self.TEST_TENANT_ID)
+        self.assertIsNone(a.username)
         s = session.Session(a)
         s.get_token()