diff --git a/translate/google/cloud/translate/client.py b/translate/google/cloud/translate/client.py
index c43acb80550b..b7fe9142d017 100644
--- a/translate/google/cloud/translate/client.py
+++ b/translate/google/cloud/translate/client.py
@@ -15,6 +15,7 @@
 """Client for interacting with the Google Cloud Translate API."""
 
 
+import httplib2
 import six
 
 from google.cloud._helpers import _to_bytes
@@ -55,6 +56,12 @@ def __init__(self, target_language=ENGLISH_ISO_639, api_key=None,
                  credentials=None, http=None):
         self.api_key = api_key
         self.target_language = target_language
+
+        if api_key is not None:
+            # If API key auth is desired, make it so that no credentials
+            # will be auto-detected by the base class constructor.
+            if http is None:
+                http = httplib2.Http()
         super(Client, self).__init__(credentials=credentials, http=http)
 
     def get_languages(self, target_language=None):
diff --git a/translate/tox.ini b/translate/tox.ini
index f33c168d61c2..168559383e71 100644
--- a/translate/tox.ini
+++ b/translate/tox.ini
@@ -6,6 +6,7 @@ envlist =
 localdeps =
     pip install --quiet --upgrade {toxinidir}/../core
 deps =
+    mock
     pytest
 covercmd =
     py.test --quiet \
diff --git a/translate/unit_tests/test_client.py b/translate/unit_tests/test_client.py
index 0fa04897af5f..2e9a23d6995e 100644
--- a/translate/unit_tests/test_client.py
+++ b/translate/unit_tests/test_client.py
@@ -27,7 +27,7 @@ def _get_target_class():
     def _make_one(self, *args, **kw):
         return self._get_target_class()(*args, **kw)
 
-    def test_ctor(self):
+    def test_constructor(self):
         from google.cloud.translate.connection import Connection
         from google.cloud.translate.client import ENGLISH_ISO_639
 
@@ -39,7 +39,7 @@ def test_ctor(self):
         self.assertIsNone(client.api_key)
         self.assertEqual(client.target_language, ENGLISH_ISO_639)
 
-    def test_ctor_non_default(self):
+    def test_constructor_non_default(self):
         from google.cloud.translate.connection import Connection
 
         http = object()
@@ -52,6 +52,22 @@ def test_ctor_non_default(self):
         self.assertEqual(self.KEY, client.api_key)
         self.assertEqual(client.target_language, target)
 
+    def test_constructor_api_key_override(self):
+        import mock
+        from google.cloud.translate.connection import Connection
+
+        target = 'ru'
+        with mock.patch('httplib2.Http') as http_ctor:
+            client = self._make_one(
+                target_language=target, api_key=self.KEY)
+
+        http_ctor.assert_called_once_with()
+        self.assertIsInstance(client._connection, Connection)
+        self.assertIsNone(client._connection.credentials)
+        self.assertIs(client._connection.http, http_ctor.return_value)
+        self.assertEqual(self.KEY, client.api_key)
+        self.assertEqual(client.target_language, target)
+
     def test_get_languages(self):
         from google.cloud.translate.client import ENGLISH_ISO_639