diff --git a/manila/share/drivers/service_instance.py b/manila/share/drivers/service_instance.py
index a28a5121eb..b873a6b844 100644
--- a/manila/share/drivers/service_instance.py
+++ b/manila/share/drivers/service_instance.py
@@ -856,7 +856,7 @@ class NeutronNetworkHelper(BaseNetworkhelper):
                     LOG.debug("Failed to delete port %(port_id)s with error: "
                               "\n %(exc)s", {"port_id": port_id, "exc": e})
 
-        if router_id and subnet_id:
+        if subnet_id:
             ports = self.neutron_api.list_ports(
                 fields=['device_id', 'device_owner'],
                 fixed_ips=['subnet_id=%s' % subnet_id])
@@ -873,17 +873,18 @@ class NeutronNetworkHelper(BaseNetworkhelper):
                     # exist that use this subnet. So, do not remove it
                     # from router.
                     return
-            try:
-                # NOTE(vponomaryov): there is no other share servers or
-                # some VMs that use this subnet. So, remove it from router.
-                self.neutron_api.router_remove_interface(
-                    router_id, subnet_id)
-            except exception.NetworkException as e:
-                if e.kwargs['code'] != 404:
-                    raise
-                LOG.debug('Subnet %(subnet_id)s is not attached to the '
-                          'router %(router_id)s.',
-                          {'subnet_id': subnet_id, 'router_id': router_id})
+            if router_id:
+                try:
+                    # NOTE(vponomaryov): there is no other share servers or
+                    # some VMs that use this subnet. So, remove it from router.
+                    self.neutron_api.router_remove_interface(
+                        router_id, subnet_id)
+                except exception.NetworkException as e:
+                    if e.kwargs['code'] != 404:
+                        raise
+                    LOG.debug('Subnet %(subnet_id)s is not attached to the '
+                              'router %(router_id)s.',
+                              {'subnet_id': subnet_id, 'router_id': router_id})
             self.neutron_api.update_subnet(subnet_id, '')
 
     @utils.synchronized(
diff --git a/manila/tests/share/drivers/test_service_instance.py b/manila/tests/share/drivers/test_service_instance.py
index 69b4616fc2..6ecc5d832d 100644
--- a/manila/tests/share/drivers/test_service_instance.py
+++ b/manila/tests/share/drivers/test_service_instance.py
@@ -1617,6 +1617,15 @@ class NeutronNetworkHelperTestCase(test.TestCase):
 
     @ddt.data(dict(), dict(subnet_id='foo'), dict(router_id='bar'))
     def test_teardown_network_no_service_data(self, server_details):
+        fake_ports = [
+            {'device_id': 'fake_device_id',
+             'device_owner': 'compute:foo'},
+        ]
+        self.mock_object(
+            service_instance.neutron.API, 'update_subnet')
+        self.mock_object(
+            service_instance.neutron.API, 'list_ports',
+            mock.Mock(return_value=fake_ports))
         instance = self._init_neutron_network_plugin()
         self.mock_object(
             service_instance.neutron.API, 'router_remove_interface')
@@ -1757,6 +1766,31 @@ class NeutronNetworkHelperTestCase(test.TestCase):
         service_instance.neutron.API.list_ports.assert_called_once_with(
             fields=['device_id', 'device_owner'], fixed_ips=['subnet_id=foo'])
 
+    def test_teardown_network_subnet_not_used_with_no_router_id(self):
+        server_details = dict(subnet_id='foo')
+        fake_ports = [
+            {'device_id': 'fake_device_id',
+             'device_owner': 'compute'},
+            {'device_id': '',
+             'device_owner': 'compute'},
+        ]
+        instance = self._init_neutron_network_plugin()
+        self.mock_object(
+            service_instance.neutron.API, 'router_remove_interface')
+        self.mock_object(
+            service_instance.neutron.API, 'update_subnet')
+        self.mock_object(
+            service_instance.neutron.API, 'list_ports',
+            mock.Mock(return_value=fake_ports))
+
+        instance.teardown_network(server_details)
+        self.assertFalse(
+            service_instance.neutron.API.router_remove_interface.called)
+        (service_instance.neutron.API.update_subnet.
+            assert_called_once_with('foo', ''))
+        service_instance.neutron.API.list_ports.assert_called_once_with(
+            fields=['device_id', 'device_owner'], fixed_ips=['subnet_id=foo'])
+
     def test_teardown_network_subnet_not_used_and_get_error_404(self):
         server_details = dict(subnet_id='foo', router_id='bar')
         fake_ports = [
diff --git a/releasenotes/notes/fix-no-router-server-0d5bf587063f22fc.yaml b/releasenotes/notes/fix-no-router-server-0d5bf587063f22fc.yaml
new file mode 100644
index 0000000000..25fd3f6b74
--- /dev/null
+++ b/releasenotes/notes/fix-no-router-server-0d5bf587063f22fc.yaml
@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Fix subnet cleanup for server instances without routers.
+    Previously, when tearing down a server instance that had no router
+    specified in its details, the associated subnet was not cleaned up because
+    the subnet cleanup code was never executed.