diff --git a/productstatus/utils.py b/productstatus/utils.py
index 63ecc26..6bdd7b6 100644
--- a/productstatus/utils.py
+++ b/productstatus/utils.py
@@ -52,6 +52,8 @@ def _serialize_datetime(self, value):
         """
         Return a time zone-aware ISO 8601 string.
         """
+        if value.tzinfo is None:
+            raise ValueError
         utc_time = value.astimezone(tz=dateutil.tz.tzutc())
         return utc_time.isoformat().replace(' ', 'T').replace('+00:00', 'Z')
 
diff --git a/setup.py b/setup.py
index 93a80fd..32de32a 100644
--- a/setup.py
+++ b/setup.py
@@ -6,13 +6,13 @@
     'author': 'MET Norway',
     'url': 'https://github.com/metno/python-productstatus-client',
     'download_url': 'https://github.com/metno/python-productstatus-client',
-    'version': '6.4.0',
+    'version': '6.5.0',
     'install_requires': [
         'nose==1.3.7',
         'requests==2.9.1',
         'python-dateutil==2.5.0',
         'httmock==1.2.4',
-        'kafka-python==1.3.1',
+        'kafka-python==1.4.2',
         'mock==2.0.0',
     ],
     'packages': find_packages(),