diff --git a/googleapiclient/_auth.py b/googleapiclient/_auth.py
index 92f2796..ada4ffb 100644
--- a/googleapiclient/_auth.py
+++ b/googleapiclient/_auth.py
@@ -19,12 +19,16 @@
 try:
     import google.auth
     import google.auth.credentials
-    import google_auth_httplib2
     HAS_GOOGLE_AUTH = True
 except ImportError:  # pragma: NO COVER
     HAS_GOOGLE_AUTH = False
 
 try:
+    import google_auth_httplib2
+except ImportError:  # pragma: NO COVER
+    google_auth_httplib2 = None
+
+try:
     import oauth2client
     import oauth2client.client
     HAS_OAUTH2CLIENT = True
@@ -88,6 +92,12 @@
 
     if HAS_GOOGLE_AUTH and isinstance(
             credentials, google.auth.credentials.Credentials):
+        if google_auth_httplib2 is None:
+            raise ValueError(
+                'Credentials from google.auth specified, but '
+                'google-api-python-client is unable to use these credentials '
+                'unless google-auth-httplib2 is installed. Please install '
+                'google-auth-httplib2.')
         return google_auth_httplib2.AuthorizedHttp(credentials,
                                                    http=build_http())
     else:
diff --git a/tests/test__auth.py b/tests/test__auth.py
index 68e7aae..003098e 100644
--- a/tests/test__auth.py
+++ b/tests/test__auth.py
@@ -68,7 +68,9 @@
 
         authorized_http = _auth.authorized_http(credentials)
 
-        self.assertIsInstance(authorized_http, google_auth_httplib2.AuthorizedHttp)
+        self.assertIsInstance(
+            authorized_http,
+            google_auth_httplib2.AuthorizedHttp)
         self.assertEqual(authorized_http.credentials, credentials)
         self.assertIsInstance(authorized_http.http, httplib2.Http)
         self.assertIsInstance(authorized_http.http.timeout, int)
@@ -138,3 +140,16 @@
     def test_default_credentials(self):
         with self.assertRaises(EnvironmentError):
             print(_auth.default_credentials())
+
+
+class TestGoogleAuthWithoutHttplib2(unittest2.TestCase):
+    def setUp(self):
+        _auth.google_auth_httplib2 = None
+
+    def tearDown(self):
+        _auth.google_auth_httplib2 = google_auth_httplib2
+
+    def test_default_credentials(self):
+        credentials = mock.Mock(spec=google.auth.credentials.Credentials)
+        with self.assertRaises(ValueError):
+            _auth.authorized_http(credentials)