diff --git a/oauth2client/appengine.py b/oauth2client/appengine.py
index 165c9b1..fc148b8 100644
--- a/oauth2client/appengine.py
+++ b/oauth2client/appengine.py
@@ -160,9 +160,8 @@
     """
     self.scope = util.scopes_to_string(scope)
 
-    super(AppAssertionCredentials, self).__init__(
-        'ignored' # assertion_type is ignore in this subclass.
-        )
+    # Assertion type is no longer used, but still in the parent class signature.
+    super(AppAssertionCredentials, self).__init__(None)
 
   @classmethod
   def from_json(cls, json):
diff --git a/oauth2client/client.py b/oauth2client/client.py
index 8517946..3370688 100644
--- a/oauth2client/client.py
+++ b/oauth2client/client.py
@@ -852,7 +852,6 @@
     assertion = self._generate_assertion()
 
     body = urllib.urlencode({
-        'assertion_type': self.assertion_type,
         'assertion': assertion,
         'grant_type': 'urn:ietf:params:oauth:grant-type:jwt-bearer',
         })
@@ -920,7 +919,7 @@
           example prn=joe@xample.org."""
 
       super(SignedJwtAssertionCredentials, self).__init__(
-          'http://oauth.net/grant_type/jwt/1.0/bearer',
+          None,
           user_agent=user_agent,
           token_uri=token_uri,
           revoke_uri=revoke_uri,
diff --git a/oauth2client/gce.py b/oauth2client/gce.py
index ad27588..c7fd7c1 100644
--- a/oauth2client/gce.py
+++ b/oauth2client/gce.py
@@ -58,9 +58,8 @@
     """
     self.scope = util.scopes_to_string(scope)
 
-    super(AppAssertionCredentials, self).__init__(
-        'ignored' # assertion_type is ignore in this subclass.
-        )
+    # Assertion type is no longer used, but still in the parent class signature.
+    super(AppAssertionCredentials, self).__init__(None)
 
   @classmethod
   def from_json(cls, json):