diff --git a/neutron/agent/l3/router_info.py b/neutron/agent/l3/router_info.py
index 4568d704e7b..beac1c8c903 100644
--- a/neutron/agent/l3/router_info.py
+++ b/neutron/agent/l3/router_info.py
@@ -567,6 +567,9 @@ class RouterInfo(object):
                     self.agent.pd.enable_subnet(self.router_id, subnet['id'],
                                      subnet['cidr'],
                                      interface_name, p['mac_address'])
+                    if (subnet['cidr'] !=
+                            lib_constants.PROVISIONAL_IPV6_PD_PREFIX):
+                        self.pd_subnets[subnet['id']] = subnet['cidr']
 
         for p in old_ports:
             self.internal_network_removed(p)
diff --git a/neutron/tests/common/l3_test_common.py b/neutron/tests/common/l3_test_common.py
index b70eb9ecf1c..4929c3fb78e 100644
--- a/neutron/tests/common/l3_test_common.py
+++ b/neutron/tests/common/l3_test_common.py
@@ -269,7 +269,9 @@ def router_append_subnet(router, count=1, ip_version=4,
     router[lib_constants.INTERFACE_KEY] = interfaces
 
 
-def router_append_pd_enabled_subnet(router, count=1):
+def router_append_pd_enabled_subnet(router, count=1, prefix=None):
+    if not prefix:
+        prefix = lib_constants.PROVISIONAL_IPV6_PD_PREFIX
     interfaces = router[lib_constants.INTERFACE_KEY]
     current = sum(netaddr.IPNetwork(subnet['cidr']).version == 6
                   for p in interfaces for subnet in p['subnets'])
@@ -288,7 +290,7 @@ def router_append_pd_enabled_subnet(router, count=1):
                                'subnet_id': subnet_id}],
                 'mac_address': str(mac_address),
                 'subnets': [{'id': subnet_id,
-                             'cidr': lib_constants.PROVISIONAL_IPV6_PD_PREFIX,
+                             'cidr': prefix,
                              'gateway_ip': '::1',
                              'ipv6_ra_mode': lib_constants.IPV6_SLAAC,
                              'subnetpool_id': lib_constants.IPV6_PD_POOL_ID}]}
@@ -308,6 +310,17 @@ def get_unassigned_pd_interfaces(router):
     return pd_intfs
 
 
+def get_assigned_pd_interfaces(router):
+    pd_intfs = []
+    for intf in router[lib_constants.INTERFACE_KEY]:
+        for subnet in intf['subnets']:
+            if (ipv6_utils.is_ipv6_pd_enabled(subnet) and
+                    subnet['cidr'] !=
+                    lib_constants.PROVISIONAL_IPV6_PD_PREFIX):
+                pd_intfs.append(intf)
+    return pd_intfs
+
+
 def assign_prefix_for_pd_interfaces(router):
     pd_intfs = []
     for ifno, intf in enumerate(router[lib_constants.INTERFACE_KEY]):
diff --git a/neutron/tests/unit/agent/l3/test_agent.py b/neutron/tests/unit/agent/l3/test_agent.py
index 33f24b97150..50b13d9465c 100644
--- a/neutron/tests/unit/agent/l3/test_agent.py
+++ b/neutron/tests/unit/agent/l3/test_agent.py
@@ -3143,6 +3143,36 @@ class TestBasicRouterOperations(BasicRouterOperationsFramework):
         gw_ifname = ri.get_external_device_name(ri.router['gw_port']['id'])
         agent.pd.add_gw_interface(ri.router['id'], gw_ifname)
 
+    @mock.patch.object(pd.PrefixDelegation, 'update_subnet')
+    @mock.patch.object(dibbler.PDDibbler, 'get_prefix', autospec=True)
+    @mock.patch.object(dibbler.os, 'getpid', return_value=1234)
+    @mock.patch.object(pd.PrefixDelegation, '_is_lla_active',
+                       return_value=True)
+    @mock.patch.object(dibbler.os, 'chmod')
+    @mock.patch.object(dibbler.shutil, 'rmtree')
+    @mock.patch.object(pd.PrefixDelegation, '_get_sync_data')
+    def test_pd_have_subnet(self, mock1, mock2, mock3, mock4,
+                            mock_getpid, mock_get_prefix,
+                            mock_pd_update_subnet):
+        '''Add one pd-enabled subnet that has already been assigned
+        '''
+        prefix = '2001:db8:10::/64'
+
+        # Initial setup
+        agent, router, ri = self._pd_setup_agent_router()
+
+        # Create one pd-enabled subnet and add router interface
+        l3_test_common.router_append_pd_enabled_subnet(router, prefix=prefix)
+        ri.process()
+
+        pd_intfs = l3_test_common.get_assigned_pd_interfaces(router)
+        subnet_id = pd_intfs[0]['subnets'][0]['id']
+
+        # Check that _process_pd_iptables_rules() is called correctly
+        self.assertEqual({subnet_id: prefix}, ri.pd_subnets)
+        ri._process_pd_iptables_rules.assert_called_once_with(prefix,
+                                                              subnet_id)
+
     @mock.patch.object(pd.PrefixDelegation, 'update_subnet')
     @mock.patch.object(dibbler.PDDibbler, 'get_prefix', autospec=True)
     @mock.patch.object(dibbler.os, 'getpid', return_value=1234)
@@ -3164,6 +3194,9 @@ class TestBasicRouterOperations(BasicRouterOperationsFramework):
         l3_test_common.router_append_pd_enabled_subnet(router)
         ri.process()
 
+        # Provisional PD prefix on startup, so nothing cached
+        self.assertEqual({}, ri.pd_subnets)
+
         # No client should be started since there is no gateway port
         self.assertFalse(self.external_process.call_count)
         self.assertFalse(mock_get_prefix.call_count)