diff --git a/apiclient/discovery.py b/apiclient/discovery.py
index 2a924a2..ee1ae54 100644
--- a/apiclient/discovery.py
+++ b/apiclient/discovery.py
@@ -71,11 +71,33 @@
   else:
     return name
 
+
 def _write_headers(self):
   # Utility no-op method for multipart media handling
   pass
 
 
+def _add_query_parameter(url, name, value):
+  """Adds a query parameter to a url
+
+  Args:
+    url: string, url to add the query parameter to.
+    name: string, query parameter name.
+    value: string, query parameter value.
+
+  Returns:
+    Updated query parameter. Does not update the url if value is None.
+  """
+  if value is None:
+    return url
+  else:
+    parsed = list(urlparse.urlparse(url))
+    q = parse_qsl(parsed[4])
+    q.append((name, value))
+    parsed[4] = urllib.urlencode(q)
+    return urlparse.urlunparse(parsed)
+
+
 def key2param(key):
   """Converts key names into parameter names.
 
@@ -131,21 +153,26 @@
 
   if http is None:
     http = httplib2.Http()
+
   requested_url = uritemplate.expand(discoveryServiceUrl, params)
+  requested_url = _add_query_parameter(requested_url, 'key', developerKey)
   logging.info('URL being requested: %s' % requested_url)
+
   resp, content = http.request(requested_url)
-  if resp.status > 400:
+
+  if resp.status >= 400:
     raise HttpError(resp, content, requested_url)
+
   try:
     service = simplejson.loads(content)
   except ValueError, e:
     logging.error('Failed to parse as JSON: ' + content)
     raise InvalidJsonError()
 
-  fn = os.path.join(os.path.dirname(__file__), 'contrib',
+  filename = os.path.join(os.path.dirname(__file__), 'contrib',
       serviceName, 'future.json')
   try:
-    f = file(fn, 'r')
+    f = file(filename, 'r')
     future = f.read()
     f.close()
   except IOError:
@@ -249,6 +276,7 @@
     "TB": 2 ** 40,
     }
 
+
 def _media_size_to_long(maxSize):
   """Convert a string media size, such as 10GB or 3TB into an integer."""
   if len(maxSize) < 2:
@@ -478,21 +506,23 @@
     setattr(method, '__doc__', ''.join(docs))
     setattr(theclass, methodName, method)
 
-  # This is a legacy method, as only Buzz and Moderator use the future.json
-  # functionality for generating _next methods. It will be kept around as long
-  # as those API versions are around, but no new APIs should depend upon it.
   def createNextMethodFromFuture(theclass, methodName, methodDesc, futureDesc):
+    """ This is a legacy method, as only Buzz and Moderator use the future.json
+    functionality for generating _next methods. It will be kept around as long
+    as those API versions are around, but no new APIs should depend upon it.
+    """
     methodName = _fix_method_name(methodName)
     methodId = methodDesc['id'] + '.next'
 
     def methodNext(self, previous):
-      """
+      """Retrieve the next page of results.
+
       Takes a single argument, 'body', which is the results
       from the last call, and returns the next set of items
       in the collection.
 
-      Returns None if there are no more items in
-      the collection.
+      Returns:
+        None if there are no more items in the collection.
       """
       if futureDesc['type'] != 'uri':
         raise UnknownLinkType(futureDesc['type'])
@@ -505,12 +535,7 @@
       except (KeyError, TypeError):
         return None
 
-      if self._developerKey:
-        parsed = list(urlparse.urlparse(url))
-        q = parse_qsl(parsed[4])
-        q.append(('key', self._developerKey))
-        parsed[4] = urllib.urlencode(q)
-        url = urlparse.urlunparse(parsed)
+      url = _add_query_parameter(url, 'key', self._developerKey)
 
       headers = {}
       headers, params, query, body = self._model.request(headers, {}, {}, None)
@@ -527,7 +552,6 @@
 
     setattr(theclass, methodName, methodNext)
 
-
   def createNextMethod(theclass, methodName, methodDesc, futureDesc):
     methodName = _fix_method_name(methodName)
     methodId = methodDesc['id'] + '.next'
diff --git a/tests/test_discovery.py b/tests/test_discovery.py
index 3070c60..5c7045e 100644
--- a/tests/test_discovery.py
+++ b/tests/test_discovery.py
@@ -27,6 +27,7 @@
 import os
 import unittest
 import urlparse
+
 try:
     from urlparse import parse_qs
 except ImportError:
@@ -44,6 +45,7 @@
 
 DATA_DIR = os.path.join(os.path.dirname(__file__), 'data')
 
+
 def datafile(filename):
   return os.path.join(DATA_DIR, filename)
 
@@ -66,19 +68,49 @@
 
 
 class DiscoveryFromDocument(unittest.TestCase):
+
   def test_can_build_from_local_document(self):
     discovery = file(datafile('buzz.json')).read()
     buzz = build_from_document(discovery, base="https://www.googleapis.com/")
     self.assertTrue(buzz is not None)
-   
+
   def test_building_with_base_remembers_base(self):
     discovery = file(datafile('buzz.json')).read()
-    
+
     base = "https://www.example.com/"
     buzz = build_from_document(discovery, base=base)
     self.assertEquals(base + "buzz/v1/", buzz._baseUrl)
 
 
+class DiscoveryFromHttp(unittest.TestCase):
+
+  def test_api_key_is_added_to_discovery_uri(self):
+    # build() will raise an HttpError on a 400, use this to pick the request uri
+    # out of the raised exception.
+    try:
+      http = HttpMockSequence([
+        ({'status': '400'}, file(datafile('zoo.json'), 'r').read()),
+        ])
+      zoo = build('zoo', 'v1', http, developerKey='foo',
+                  discoveryServiceUrl='http://example.com')
+      self.fail('Should have raised an exception.')
+    except HttpError, e:
+      self.assertEqual(e.uri, 'http://example.com?key=foo')
+
+  def test_api_key_of_none_is_not_added_to_discovery_uri(self):
+    # build() will raise an HttpError on a 400, use this to pick the request uri
+    # out of the raised exception.
+    try:
+      http = HttpMockSequence([
+        ({'status': '400'}, file(datafile('zoo.json'), 'r').read()),
+        ])
+      zoo = build('zoo', 'v1', http, developerKey=None,
+                  discoveryServiceUrl='http://example.com')
+      self.fail('Should have raised an exception.')
+    except HttpError, e:
+      self.assertEqual(e.uri, 'http://example.com')
+
+
 class Discovery(unittest.TestCase):
 
   def test_method_error_checking(self):
@@ -128,12 +160,15 @@
     http = HttpMock(datafile('zoo.json'), {'status': '200'})
     zoo = build('zoo', 'v1', http)
 
-    request = zoo.query(q="foo", i=1.0, n=1.0, b=0, a=[1,2,3], o={'a':1}, e='bar')
+    request = zoo.query(
+        q="foo", i=1.0, n=1.0, b=0, a=[1,2,3], o={'a':1}, e='bar')
     self._check_query_types(request)
-    request = zoo.query(q="foo", i=1, n=1, b=False, a=[1,2,3], o={'a':1}, e='bar')
+    request = zoo.query(
+        q="foo", i=1, n=1, b=False, a=[1,2,3], o={'a':1}, e='bar')
     self._check_query_types(request)
 
-    request = zoo.query(q="foo", i="1", n="1", b="", a=[1,2,3], o={'a':1}, e='bar')
+    request = zoo.query(
+        q="foo", i="1", n="1", b="", a=[1,2,3], o={'a':1}, e='bar')
     self._check_query_types(request)
 
   def test_optional_stack_query_parameters(self):
@@ -160,7 +195,8 @@
       ])
     http = tunnel_patch(http)
     zoo = build('zoo', 'v1', http)
-    resp = zoo.animals().patch(name='lion', body='{"description": "foo"}').execute()
+    resp = zoo.animals().patch(
+        name='lion', body='{"description": "foo"}').execute()
 
     self.assertTrue('x-http-method-override' in resp)
 
@@ -277,7 +313,8 @@
     zoo = build('zoo', 'v1', self.http)
 
     request = zoo.animals().insert(media_body=datafile('small.png'), body={})
-    self.assertTrue(request.headers['content-type'].startswith('multipart/related'))
+    self.assertTrue(request.headers['content-type'].startswith(
+        'multipart/related'))
     self.assertEquals('--==', request.body[0:4])
 
   def test_media_capable_method_without_media(self):
@@ -308,7 +345,8 @@
     self.http = HttpMock(datafile('tasks.json'), {'status': '200'})
     tasks = build('tasks', 'v1', self.http)
     request = tasks.tasklists().list()
-    next_request = tasks.tasklists().list_next(request, {'nextPageToken': '123abc'})
+    next_request = tasks.tasklists().list_next(
+        request, {'nextPageToken': '123abc'})
     parsed = list(urlparse.urlparse(next_request.uri))
     q = parse_qs(parsed[4])
     self.assertEqual(q['pageToken'][0], '123abc')
@@ -318,7 +356,9 @@
     service = build('latitude', 'v1', self.http)
     request = service.currentLocation().get()
 
+
 class DeveloperKey(unittest.TestCase):
+
   def test_param(self):
     self.http = HttpMock(datafile('buzz.json'), {'status': '200'})
     buzz = build('buzz', 'v1', self.http, developerKey='foobie_bletch')