diff --git a/ceilometer/compute/notifications/instance.py b/ceilometer/compute/notifications/instance.py
index 2146dd4bb..f8e600614 100644
--- a/ceilometer/compute/notifications/instance.py
+++ b/ceilometer/compute/notifications/instance.py
@@ -36,7 +36,7 @@ class UserMetadataAwareInstanceNotificationBase(
 
     def process_notification(self, message):
         instance_properties = self.get_instance_properties(message)
-        if 'metadata' in instance_properties:
+        if isinstance(instance_properties.get('metadata'), dict):
             src_metadata = instance_properties['metadata']
             del instance_properties['metadata']
             util.add_reserved_user_metadata(src_metadata, instance_properties)
diff --git a/ceilometer/tests/compute/notifications/test_instance.py b/ceilometer/tests/compute/notifications/test_instance.py
index 725b65cc0..b63af6d79 100644
--- a/ceilometer/tests/compute/notifications/test_instance.py
+++ b/ceilometer/tests/compute/notifications/test_instance.py
@@ -166,6 +166,55 @@ INSTANCE_EXISTS = {
     u'timestamp': u'2012-05-08 16:03:44.122481',
 }
 
+INSTANCE_EXISTS_METADATA_LIST = {
+    u'_context_auth_token': None,
+    u'_context_is_admin': True,
+    u'_context_project_id': None,
+    u'_context_quota_class': None,
+    u'_context_read_deleted': u'no',
+    u'_context_remote_address': None,
+    u'_context_request_id': u'req-659a8eb2-4372-4c01-9028-ad6e40b0ed22',
+    u'_context_roles': [u'admin'],
+    u'_context_timestamp': u'2012-05-08T16:03:43.760204',
+    u'_context_user_id': None,
+    u'event_type': u'compute.instance.exists',
+    u'message_id': u'4b884c03-756d-4c06-8b42-80b6def9d302',
+    u'payload': {u'audit_period_beginning': u'2012-05-08 15:00:00',
+                 u'audit_period_ending': u'2012-05-08 16:00:00',
+                 u'bandwidth': {},
+                 u'created_at': u'2012-05-07 22:16:18',
+                 u'deleted_at': u'',
+                 u'disk_gb': 0,
+                 u'display_name': u'testme',
+                 u'image_ref_url': u'http://10.0.2.15:9292/images/UUID',
+                 u'instance_id': u'3a513875-95c9-4012-a3e7-f90c678854e5',
+                 u'instance_type': u'm1.tiny',
+                 u'instance_type_id': 2,
+                 u'launched_at': u'2012-05-07 23:01:27',
+                 u'memory_mb': 512,
+                 u'state': u'active',
+                 u'state_description': u'',
+                 u'tenant_id': u'7c150a59fe714e6f9263774af9688f0e',
+                 u'user_id': u'1e3ce043029547f1a61c1996d1a531a2',
+                 u'reservation_id': u'1e3ce043029547f1a61c1996d1a531a3',
+                 u'vcpus': 1,
+                 u'root_gb': 0,
+                 u'metadata': [],
+                 u'ephemeral_gb': 0,
+                 u'host': u'compute-host-name',
+                 u'availability_zone': u'1e3ce043029547f1a61c1996d1a531a4',
+                 u'os_type': u'linux?',
+                 u'architecture': u'x86',
+                 u'image_ref': u'UUID',
+                 u'kernel_id': u'1e3ce043029547f1a61c1996d1a531a5',
+                 u'ramdisk_id': u'1e3ce043029547f1a61c1996d1a531a6',
+                 },
+    u'priority': u'INFO',
+    u'publisher_id': u'compute.vagrant-precise',
+    u'timestamp': u'2012-05-08 16:03:44.122481',
+}
+
+
 INSTANCE_FINISH_RESIZE_END = {
     u'_context_roles': [u'admin'],
     u'_context_request_id': u'req-e3f71bb9-e9b9-418b-a9db-a5950c851b25',
@@ -627,6 +676,11 @@ class TestNotifications(test.BaseTestCase):
         counters = list(ic.process_notification(INSTANCE_EXISTS))
         self.assertEqual(1, len(counters))
 
+    def test_instance_exists_metadata_list(self):
+        ic = instance.Instance()
+        counters = list(ic.process_notification(INSTANCE_EXISTS_METADATA_LIST))
+        self.assertEqual(1, len(counters))
+
     def test_instance_exists_flavor(self):
         ic = instance.Instance()
         counters = list(ic.process_notification(INSTANCE_EXISTS))