diff --git a/monasca_api/common/repositories/model/sub_alarm_definition.py b/monasca_api/common/repositories/model/sub_alarm_definition.py
index e5c517e..5b0170d 100644
--- a/monasca_api/common/repositories/model/sub_alarm_definition.py
+++ b/monasca_api/common/repositories/model/sub_alarm_definition.py
@@ -49,9 +49,8 @@ class SubAlarmDefinition(object):
             self.deterministic = str(row['is_deterministic']) == '1'
 
         if sub_expr:
-            # id is not used for compare or hash.
-            self.id = ''
             # Must be injected.
+            self.id = ''
             self.alarm_definition_id = ''
             self.metric_name = sub_expr.metric_name
             self.dimensions_str = sub_expr.dimensions_str
diff --git a/monasca_api/common/repositories/sqla/alarm_definitions_repository.py b/monasca_api/common/repositories/sqla/alarm_definitions_repository.py
index 8296301..a0edafe 100644
--- a/monasca_api/common/repositories/sqla/alarm_definitions_repository.py
+++ b/monasca_api/common/repositories/sqla/alarm_definitions_repository.py
@@ -683,6 +683,7 @@ class AlarmDefinitionsRepository(sql_repository.SQLRepository,
         for sub_expr in sub_expr_list:
             sad = sub_alarm_definition.SubAlarmDefinition(
                 sub_expr=sub_expr)
+            # Note: the .id yet needs to be set (see below)
             # Inject the alarm definition id.
             sad.alarm_definition_id = alarm_definition_id.decode('utf8')
             new_sub_alarm_defs_set.add(sad)
@@ -710,6 +711,8 @@ class AlarmDefinitionsRepository(sql_repository.SQLRepository,
                     changed_sub_alarm_defs_by_id[
                         old_or_changed.id] = (
                         new_or_changed)
+                    # inject the missing ID (taken from the old), otherwise updates will not work
+                    new_or_changed.id = old_or_changed.id
         old_or_changed_sub_alarm_defs_set = (
             old_or_changed_sub_alarm_defs_set -
             old_or_changed_sub_alarm_defs_set_to_remove
diff --git a/monasca_api/tests/test_alarms.py b/monasca_api/tests/test_alarms.py
index 5eb1225..41c3c4c 100644
--- a/monasca_api/tests/test_alarms.py
+++ b/monasca_api/tests/test_alarms.py
@@ -500,7 +500,7 @@ class TestAlarmDefinition(AlarmTestBase):
         sub_expression = {'11111': {u'expression': expr,
                                     u'function': 'max',
                                     u'metricDefinition': {
-                                        u'dimensions': {u'uname': 'host'},
+                                        u'dimensions': {'hostname': 'host'},
                                         u'name': 'test.metric'},
                                     u'operator': 'gte',
                                     u'period': 60,
diff --git a/monasca_api/v2/reference/alarm_definitions.py b/monasca_api/v2/reference/alarm_definitions.py
index 7e68b77..d851d5d 100644
--- a/monasca_api/v2/reference/alarm_definitions.py
+++ b/monasca_api/v2/reference/alarm_definitions.py
@@ -458,16 +458,13 @@ class AlarmDefinitions(alarm_definitions_api_v2.AlarmDefinitionsV2API,
 
         sub_alarm_def_update_dict = {}
         for id, sub_alarm_def in sub_alarm_def_dict.items():
-            dimensions = {}
-            for name, value in sub_alarm_def.dimensions.items():
-                dimensions[u'uname'] = value
             sub_alarm_def_update_dict[sub_alarm_def.id] = {}
             sub_alarm_def_update_dict[sub_alarm_def.id][u'function'] = (
                 sub_alarm_def.function)
             sub_alarm_def_update_dict[sub_alarm_def.id][
                 u'metricDefinition'] = (
                 {u'name': sub_alarm_def.metric_name,
-                 u'dimensions': dimensions})
+                 u'dimensions': sub_alarm_def.dimensions.copy()})
             sub_alarm_def_update_dict[sub_alarm_def.id][u'operator'] = (
                 sub_alarm_def.operator)
             sub_alarm_def_update_dict[sub_alarm_def.id][u'threshold'] = (