diff --git a/neutron/plugins/ml2/drivers/agent/_common_agent.py b/neutron/plugins/ml2/drivers/agent/_common_agent.py
index 4e5b15ac950..c6efd43140a 100644
--- a/neutron/plugins/ml2/drivers/agent/_common_agent.py
+++ b/neutron/plugins/ml2/drivers/agent/_common_agent.py
@@ -366,7 +366,7 @@ class CommonAgentLoop(service.Service):
         returned because this means it is new.
         """
         return {device for device, timestamp in timestamps.items()
-                if previous_timestamps.get(device) and
+                if device in previous_timestamps and
                 timestamp != previous_timestamps.get(device)}
 
     def scan_devices(self, previous, sync):
diff --git a/neutron/tests/unit/plugins/ml2/drivers/agent/test__common_agent.py b/neutron/tests/unit/plugins/ml2/drivers/agent/test__common_agent.py
index c7091bbf5cf..d56796269cb 100644
--- a/neutron/tests/unit/plugins/ml2/drivers/agent/test__common_agent.py
+++ b/neutron/tests/unit/plugins/ml2/drivers/agent/test__common_agent.py
@@ -233,6 +233,23 @@ class TestCommonAgentLoop(base.BaseTestCase):
         self._test_scan_devices(previous, updated, fake_current, expected,
                                 sync=False)
 
+    def test_scan_devices_timestamp_triggers_updated_None_to_something(self):
+        previous = {'current': set([1, 2]),
+                    'updated': set(),
+                    'added': set(),
+                    'removed': set(),
+                    'timestamps': {2: None}}
+        fake_current = set([1, 2])
+        updated = set()
+        expected = {'current': set([1, 2]),
+                    'updated': set([2]),
+                    'added': set(),
+                    'removed': set(),
+                    'timestamps': {2: 1000}}
+
+        self._test_scan_devices(previous, updated, fake_current, expected,
+                                sync=False, fake_ts_current={2: 1000})
+
     def test_scan_devices_timestamp_triggers_updated(self):
         previous = {'current': set([1, 2]),
                     'updated': set(),