diff --git a/ceilometer/tests/pipeline_base.py b/ceilometer/tests/pipeline_base.py
index 831c1838e..f01bf6c2e 100644
--- a/ceilometer/tests/pipeline_base.py
+++ b/ceilometer/tests/pipeline_base.py
@@ -1441,3 +1441,55 @@ class BasePipelineTestCase(test.BaseTestCase):
         pipe.flush(None)
         publisher = pipeline_manager.pipelines[0].publishers[0]
         self.assertEqual(1, len(publisher.samples))
+
+    def test_aggregator_without_authentication(self):
+        transformer_cfg = [
+            {
+                'name': 'aggregator',
+                'parameters': {'size': 2},
+            },
+        ]
+        self._set_pipeline_cfg('transformers', transformer_cfg)
+        self._set_pipeline_cfg('counters', ['storage.objects.outgoing.bytes'])
+        counters = [
+            sample.Sample(
+                name='storage.objects.outgoing.bytes',
+                type=sample.TYPE_DELTA,
+                volume=26,
+                unit='B',
+                user_id=None,
+                project_id=None,
+                resource_id='test_resource',
+                timestamp=timeutils.utcnow().isoformat(),
+                resource_metadata={'version': '1.0'}
+            ),
+            sample.Sample(
+                name='storage.objects.outgoing.bytes',
+                type=sample.TYPE_DELTA,
+                volume=16,
+                unit='B',
+                user_id=None,
+                project_id=None,
+                resource_id='test_resource',
+                timestamp=timeutils.utcnow().isoformat(),
+                resource_metadata={'version': '2.0'}
+            )
+        ]
+
+        pipeline_manager = pipeline.PipelineManager(self.pipeline_cfg,
+                                                    self.transformer_manager)
+        pipe = pipeline_manager.pipelines[0]
+
+        pipe.publish_samples(None, [counters[0]])
+        pipe.flush(None)
+        publisher = pipe.publishers[0]
+        self.assertEqual(0, len(publisher.samples))
+
+        pipe.publish_samples(None, [counters[1]])
+        pipe.flush(None)
+        publisher = pipe.publishers[0]
+
+        self.assertEqual(1, len(publisher.samples))
+        self.assertEqual(42, getattr(publisher.samples[0], 'volume'))
+        self.assertEqual("test_resource", getattr(publisher.samples[0],
+                                                  'resource_id'))
diff --git a/ceilometer/transformer/conversions.py b/ceilometer/transformer/conversions.py
index 6c4fc58e4..38cf929ea 100644
--- a/ceilometer/transformer/conversions.py
+++ b/ceilometer/transformer/conversions.py
@@ -214,8 +214,13 @@ class AggregatorTransformer(ScalingTransformer):
             self.key_attributes.append(name)
 
     def _get_unique_key(self, s):
-        non_aggregated_keys = "-".join([getattr(s, field)
-                                        for field in self.key_attributes])
+        # NOTE(arezmerita): in samples generated by ceilometer middleware,
+        # when accessing without authentication publicly readable/writable
+        # swift containers, the project_id and the user_id are missing.
+        # They will be replaced by <undefined> for unique key construction.
+        keys = ['<undefined>' if getattr(s, f) is None else getattr(s, f)
+                for f in self.key_attributes]
+        non_aggregated_keys = "-".join(keys)
         # NOTE(sileht): it assumes, a meter always have the same unit/type
         return "%s-%s-%s" % (s.name, s.resource_id, non_aggregated_keys)