diff --git a/neutron/agent/dhcp/agent.py b/neutron/agent/dhcp/agent.py
index bb3ed49b6e8..b2793d3b059 100644
--- a/neutron/agent/dhcp/agent.py
+++ b/neutron/agent/dhcp/agent.py
@@ -1050,11 +1050,12 @@ class NetworkCache(object):
         "self._deleted_ports" and "self._deleted_ports_ts".
         """
         timestamp_min = timeutils.utcnow_ts() - DELETED_PORT_MAX_AGE
-        idx = None
-        for idx, (ts, port_id) in enumerate(self._deleted_ports_ts):
+        idx = 0
+        for (ts, port_id) in self._deleted_ports_ts:
             if ts > timestamp_min:
                 break
             self._deleted_ports.remove(port_id)
+            idx += 1
 
         if idx:
             self._deleted_ports_ts = self._deleted_ports_ts[idx:]
diff --git a/neutron/tests/unit/agent/dhcp/test_agent.py b/neutron/tests/unit/agent/dhcp/test_agent.py
index 70079920abe..a5726963c4b 100644
--- a/neutron/tests/unit/agent/dhcp/test_agent.py
+++ b/neutron/tests/unit/agent/dhcp/test_agent.py
@@ -1719,6 +1719,12 @@ class TestNetworkCache(base.BaseTestCase):
         nc = dhcp_agent.NetworkCache()
         nc.add_to_deleted_ports(fake_port1.id)
         utils.wait_until_true(lambda: nc._deleted_ports == set(), timeout=7)
+        self.assertEqual([], self.nc._deleted_ports_ts)
+
+        # check the second iteration is ok too
+        nc.add_to_deleted_ports(fake_port2.id)
+        utils.wait_until_true(lambda: nc._deleted_ports == set(), timeout=7)
+        self.assertEqual([], self.nc._deleted_ports_ts)
 
 
 class FakePort1(object):