diff --git a/neutron/db/agents_db.py b/neutron/db/agents_db.py
index e282173684b..3b5e5cd2ab8 100644
--- a/neutron/db/agents_db.py
+++ b/neutron/db/agents_db.py
@@ -78,10 +78,8 @@ AZ_ATTRIBUTE_MAP = {
 def get_availability_zones_by_agent_type(context, agent_type,
                                          availability_zones):
     """Get list of availability zones based on agent type"""
-
-    agents = agent_obj.Agent.get_agents_by_availability_zones_and_agent_type(
+    return agent_obj.Agent.get_availability_zones_by_agent_type(
         context, agent_type=agent_type, availability_zones=availability_zones)
-    return set(agent.availability_zone for agent in agents)
 
 
 class AgentAvailabilityZoneMixin(az_ext.AvailabilityZonePluginBase):
diff --git a/neutron/objects/agent.py b/neutron/objects/agent.py
index 62b7daea14b..6b4d1730053 100644
--- a/neutron/objects/agent.py
+++ b/neutron/objects/agent.py
@@ -154,15 +154,18 @@ class Agent(base.NeutronDbObject):
 
     @classmethod
     @db_api.CONTEXT_READER
-    def get_agents_by_availability_zones_and_agent_type(
+    def get_availability_zones_by_agent_type(
             cls, context, agent_type, availability_zones):
-        query = context.session.query(agent_model.Agent).filter_by(
-            agent_type=agent_type).group_by(
-                agent_model.Agent.availability_zone)
+        query = context.session.query(
+            agent_model.Agent.availability_zone,
+            agent_model.Agent.agent_type)
         query = query.filter(
-            agent_model.Agent.availability_zone.in_(availability_zones)).all()
-        agents = [cls._load_object(context, record) for record in query]
-        return agents
+            agent_model.Agent.availability_zone.in_(availability_zones),
+            agent_model.Agent.agent_type == agent_type)
+        agents = query.group_by(
+            agent_model.Agent.availability_zone,
+            agent_model.Agent.agent_type).all()
+        return [agent[0] for agent in agents]
 
     @classmethod
     def get_objects_by_agent_mode(cls, context, agent_mode=None, **kwargs):
diff --git a/neutron/tests/functional/objects/test_agent.py b/neutron/tests/functional/objects/test_agent.py
new file mode 100644
index 00000000000..2cd8f0a8de4
--- /dev/null
+++ b/neutron/tests/functional/objects/test_agent.py
@@ -0,0 +1,85 @@
+# Copyright 2021 Red Hat, Inc.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from collections import defaultdict
+
+from neutron_lib import context as n_context
+from neutron_lib.db import api as db_api
+from oslo_utils import timeutils
+from oslo_utils import uuidutils
+
+from neutron.objects import agent as agent_obj
+from neutron.tests.unit import testlib_api
+
+
+class _AgentSql(testlib_api.SqlTestCase):
+
+    def setUp(self):
+        super().setUp()
+        self.context = n_context.get_admin_context()
+
+    @db_api.CONTEXT_WRITER
+    def _create_agent(self, context, agent_type, az, host=None):
+        host = host or uuidutils.generate_uuid()
+        agent = agent_obj.Agent(context, agent_type=agent_type,
+                                availability_zone=az, host=host,
+                                binary=uuidutils.generate_uuid(),
+                                topic=uuidutils.generate_uuid(),
+                                admin_state_up=True,
+                                created_at=timeutils.utcnow(),
+                                started_at=timeutils.utcnow(),
+                                heartbeat_timestamp=timeutils.utcnow(),
+                                configurations='{}',
+                                load=0,
+                                )
+        agent.create()
+
+    def test_get_agents_by_availability_zones_and_agent_type(self):
+        self.agents = defaultdict(dict)
+        agent_types = ('dhcp', 'ovs', 'l3agent')
+        azs = ('az1', 'az2', 'az3')
+        for type_ in agent_types:
+            for az in azs:
+                # Create up to 5 agents per AZ and agent type. That will check
+                # the query GROUP BY clause.
+                for _ in range(5):
+                    self._create_agent(self.context, type_, az)
+
+        method = agent_obj.Agent.get_availability_zones_by_agent_type
+        for type_ in agent_types:
+            for az in azs:
+                res_azs = method(self.context, type_, [az])
+                self.assertEqual(1, len(res_azs))
+                self.assertEqual(az, res_azs[0])
+
+        # Non-existing types, correct AZs
+        for type_ in ('type1', 'type2'):
+            for az in azs:
+                res_azs = method(self.context, type_, [az])
+                self.assertEqual(0, len(res_azs))
+
+        # Correct types, non-existing AZs
+        for type_ in agent_types:
+            for az in ('az23', 'az42'):
+                res_azs = method(self.context, type_, [az])
+                self.assertEqual(0, len(res_azs))
+
+
+class TestAgentMySQL(testlib_api.MySQLTestCaseMixin, _AgentSql):
+    pass
+
+
+class TestAgentPostgreSQL(testlib_api.PostgreSQLTestCaseMixin, _AgentSql):
+    pass