diff --git a/CHANGELOG b/CHANGELOG
index 0882e63..ba72d15 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,10 @@
+v1.6.4
+  Version 1.6.4
+
+  Bugfix release
+
+  - Warn when google-auth credentials are used but google-auth-httplib2 isn't available. (#443)
+
 v1.6.3
   Version 1.6.3
 
diff --git a/googleapiclient/__init__.py b/googleapiclient/__init__.py
index 97977bb..184219a 100644
--- a/googleapiclient/__init__.py
+++ b/googleapiclient/__init__.py
@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-__version__ = "1.6.3"
+__version__ = "1.6.4"
 
 # Set default logging handler to avoid "No handler found" warnings.
 import logging