diff --git a/gcloud/datastore/helpers.py b/gcloud/datastore/helpers.py
index ccef721e97b4d..39ddd9d222a63 100644
--- a/gcloud/datastore/helpers.py
+++ b/gcloud/datastore/helpers.py
@@ -37,7 +37,7 @@ def get_protobuf_attribute_and_value(val):
   """
 
   if isinstance(val, datetime):
-    name, value = 'timestamp_microseconds', time.mktime(val.timetuple())
+    name, value = 'timestamp_microseconds', long(time.mktime(val.timetuple()))
   elif isinstance(val, Key):
     name, value = 'key', val.to_protobuf()
   elif isinstance(val, bool):
diff --git a/gcloud/datastore/test_helpers.py b/gcloud/datastore/test_helpers.py
index 262ebe511a9a3..5679d473729fb 100644
--- a/gcloud/datastore/test_helpers.py
+++ b/gcloud/datastore/test_helpers.py
@@ -37,7 +37,7 @@ def test_get_protobuf_value(self):
         (long(), int()),
         (float(), float()),
         (bool(), bool()),
-        (now, time.mktime(now.timetuple())),
+        (now, long(time.mktime(now.timetuple()))),
         (Key(), Key().to_protobuf()),
         )