diff --git a/ceilometer/api/controllers/v2.py b/ceilometer/api/controllers/v2.py
index e0a4c0839..5058c2454 100644
--- a/ceilometer/api/controllers/v2.py
+++ b/ceilometer/api/controllers/v2.py
@@ -272,9 +272,10 @@ class Query(_Base):
 
 
 class ProjectNotAuthorized(ClientSideError):
-    def __init__(self, id):
+    def __init__(self, id, aspect='project'):
+        params = dict(aspect=aspect, id=id)
         super(ProjectNotAuthorized, self).__init__(
-            _("Not Authorized to access project %s") % id,
+            _("Not Authorized to access %(aspect)s %(id)s") % params,
             status_code=401)
 
 
@@ -2037,15 +2038,24 @@ class AlarmsController(rest.RestController):
         now = timeutils.utcnow()
 
         data.alarm_id = str(uuid.uuid4())
-        user, project = acl.get_limited_to(pecan.request.headers)
-        if user:
-            data.user_id = user
-        elif data.user_id == wtypes.Unset:
-            data.user_id = pecan.request.headers.get('X-User-Id')
-        if project:
-            data.project_id = project
-        elif data.project_id == wtypes.Unset:
-            data.project_id = pecan.request.headers.get('X-Project-Id')
+        user_limit, project_limit = acl.get_limited_to(pecan.request.headers)
+
+        def _set_ownership(aspect, owner_limitation, header):
+            attr = '%s_id' % aspect
+            requested_owner = getattr(data, attr)
+            explicit_owner = requested_owner != wtypes.Unset
+            caller = pecan.request.headers.get(header)
+            if (owner_limitation and explicit_owner
+                    and requested_owner != caller):
+                raise ProjectNotAuthorized(requested_owner, aspect)
+
+            actual_owner = (owner_limitation or
+                            requested_owner if explicit_owner else caller)
+            setattr(data, attr, actual_owner)
+
+        _set_ownership('user', user_limit, 'X-User-Id')
+        _set_ownership('project', project_limit, 'X-Project-Id')
+
         data.timestamp = now
         data.state_timestamp = now
 
diff --git a/ceilometer/tests/api/v2/test_alarm_scenarios.py b/ceilometer/tests/api/v2/test_alarm_scenarios.py
index 4758c492b..6693dbc72 100644
--- a/ceilometer/tests/api/v2/test_alarm_scenarios.py
+++ b/ceilometer/tests/api/v2/test_alarm_scenarios.py
@@ -857,6 +857,90 @@ class TestAlarms(FunctionalTest,
                          alarms[0].project_id)
         self._verify_alarm(json, alarms[0], 'added_alarm')
 
+    @staticmethod
+    def _alarm_representation_owned_by(identifiers):
+        json = {
+            'name': 'added_alarm',
+            'enabled': False,
+            'type': 'threshold',
+            'ok_actions': ['http://something/ok'],
+            'threshold_rule': {
+                'meter_name': 'ameter',
+                'query': [{'field': 'metadata.field',
+                           'op': 'eq',
+                           'value': '5',
+                           'type': 'string'}],
+                'comparison_operator': 'le',
+                'statistic': 'count',
+                'threshold': 50,
+                'evaluation_periods': 3,
+                'period': 180,
+            }
+        }
+        for aspect, id in identifiers.iteritems():
+            json['%s_id' % aspect] = id
+        return json
+
+    def _do_test_post_alarm_as_nonadmin_on_behalf_of_another(self,
+                                                             identifiers):
+        """Test that posting an alarm as non-admin on behalf of another
+        user/project fails with an explicit 401 instead of reverting
+        to the requestor's identity.
+        """
+        json = self._alarm_representation_owned_by(identifiers)
+        headers = {}
+        headers.update(self.auth_headers)
+        headers['X-Roles'] = 'demo'
+        resp = self.post_json('/alarms', params=json, status=401,
+                              headers=headers)
+        aspect = 'user' if 'user' in identifiers else 'project'
+        params = dict(aspect=aspect, id=identifiers[aspect])
+        self.assertEqual("Not Authorized to access %(aspect)s %(id)s" % params,
+                         jsonutils.loads(resp.body)['error_message']
+                         ['faultstring'])
+
+    def test_post_alarm_as_nonadmin_on_behalf_of_another_user(self):
+        identifiers = dict(user='auseridthatisnotmine')
+        self._do_test_post_alarm_as_nonadmin_on_behalf_of_another(identifiers)
+
+    def test_post_alarm_as_nonadmin_on_behalf_of_another_project(self):
+        identifiers = dict(project='aprojectidthatisnotmine')
+        self._do_test_post_alarm_as_nonadmin_on_behalf_of_another(identifiers)
+
+    def test_post_alarm_as_nonadmin_on_behalf_of_another_creds(self):
+        identifiers = dict(user='auseridthatisnotmine',
+                           project='aprojectidthatisnotmine')
+        self._do_test_post_alarm_as_nonadmin_on_behalf_of_another(identifiers)
+
+    def _do_test_post_alarm_as_nonadmin_on_behalf_of_self(self, identifiers):
+        """Test posting an alarm as non-admin on behalf of own user/project
+        creates alarm associated with the requestor's identity.
+        """
+        json = self._alarm_representation_owned_by(identifiers)
+        headers = {}
+        headers.update(self.auth_headers)
+        headers['X-Roles'] = 'demo'
+        self.post_json('/alarms', params=json, status=201, headers=headers)
+        alarms = list(self.conn.get_alarms(enabled=False))
+        self.assertEqual(1, len(alarms))
+        self.assertEqual(alarms[0].user_id,
+                         self.auth_headers['X-User-Id'])
+        self.assertEqual(alarms[0].project_id,
+                         self.auth_headers['X-Project-Id'])
+
+    def test_post_alarm_as_nonadmin_on_behalf_of_own_user(self):
+        identifiers = dict(user=self.auth_headers['X-User-Id'])
+        self._do_test_post_alarm_as_nonadmin_on_behalf_of_self(identifiers)
+
+    def test_post_alarm_as_nonadmin_on_behalf_of_own_project(self):
+        identifiers = dict(project=self.auth_headers['X-Project-Id'])
+        self._do_test_post_alarm_as_nonadmin_on_behalf_of_self(identifiers)
+
+    def test_post_alarm_as_nonadmin_on_behalf_of_own_creds(self):
+        identifiers = dict(user=self.auth_headers['X-User-Id'],
+                           project=self.auth_headers['X-Project-Id'])
+        self._do_test_post_alarm_as_nonadmin_on_behalf_of_self(identifiers)
+
     def test_post_alarm_combination(self):
         json = {
             'enabled': False,