diff --git a/ceilometer/api/controllers/v2/alarms.py b/ceilometer/api/controllers/v2/alarms.py
index a0c6ca2ad..9334cf37e 100644
--- a/ceilometer/api/controllers/v2/alarms.py
+++ b/ceilometer/api/controllers/v2/alarms.py
@@ -440,11 +440,12 @@ class Alarm(base.Base):
 
         ALARMS_RULES[alarm.type].plugin.validate_alarm(alarm)
 
-        tc_names = [tc.name for tc in alarm.time_constraints]
-        if len(tc_names) > len(set(tc_names)):
-            error = _("Time constraint names must be "
-                      "unique for a given alarm.")
-            raise base.ClientSideError(error)
+        if alarm.time_constraints:
+            tc_names = [tc.name for tc in alarm.time_constraints]
+            if len(tc_names) > len(set(tc_names)):
+                error = _("Time constraint names must be "
+                          "unique for a given alarm.")
+                raise base.ClientSideError(error)
 
         return alarm
 
@@ -513,7 +514,9 @@ class Alarm(base.Base):
             if k.endswith('_rule'):
                 del d[k]
         d['rule'] = getattr(self, "%s_rule" % self.type).as_dict()
-        d['time_constraints'] = [tc.as_dict() for tc in self.time_constraints]
+        if self.time_constraints:
+            d['time_constraints'] = [tc.as_dict()
+                                     for tc in self.time_constraints]
         return d
 
 Alarm.add_attributes(**{"%s_rule" % ext.name: ext.plugin
diff --git a/ceilometer/tests/api/v2/test_alarm_scenarios.py b/ceilometer/tests/api/v2/test_alarm_scenarios.py
index 1f8e5dee2..7a46f6752 100644
--- a/ceilometer/tests/api/v2/test_alarm_scenarios.py
+++ b/ceilometer/tests/api/v2/test_alarm_scenarios.py
@@ -458,6 +458,19 @@ class TestAlarms(v2.FunctionalTest,
         alarms = list(self.alarm_conn.get_alarms())
         self.assertEqual(4, len(alarms))
 
+    def test_post_alarm_null_time_constraint(self):
+        json = {
+            'name': 'added_alarm_invalid_constraint_duration',
+            'type': 'threshold',
+            'time_constraints': None,
+            'threshold_rule': {
+                'meter_name': 'ameter',
+                'threshold': 300.0
+            }
+        }
+        self.post_json('/alarms', params=json, status=201,
+                       headers=self.auth_headers)
+
     def test_post_invalid_alarm_time_constraint_duration(self):
         json = {
             'name': 'added_alarm_invalid_constraint_duration',