diff --git a/neutron/services/segments/plugin.py b/neutron/services/segments/plugin.py
index 79526dc8083..fb88d2a7d9d 100644
--- a/neutron/services/segments/plugin.py
+++ b/neutron/services/segments/plugin.py
@@ -260,10 +260,10 @@ class NovaSegmentNotifier(object):
             total += int(netaddr.IPAddress(pool['end']) -
                          netaddr.IPAddress(pool['start'])) + 1
         if total:
-            if subnet['gateway_ip']:
+            if subnet.get('gateway_ip'):
                 total += 1
                 reserved += 1
-            if subnet['enable_dhcp']:
+            if subnet.get('enable_dhcp'):
                 reserved += 1
         return total, reserved
 
@@ -560,7 +560,7 @@ class SegmentHostRoutes(object):
                 context=context,
                 ip_version=netaddr.IPNetwork(subnet['cidr']).version,
                 network_id=subnet['network_id'],
-                segment_id=subnet['segment_id'],
+                segment_id=segment_id,
                 host_routes=copy.deepcopy(host_routes),
                 gateway_ip=gateway_ip)
             if (not host_routes or
@@ -572,11 +572,14 @@ class SegmentHostRoutes(object):
     def host_routes_before_update(self, resource, event, trigger, **kwargs):
         context = kwargs['context']
         subnet, original_subnet = kwargs['request'], kwargs['original_subnet']
-        segment_id = subnet.get('segment_id', original_subnet['segment_id'])
-        gateway_ip = subnet.get('gateway_ip', original_subnet['gateway_ip'])
-        host_routes = subnet.get('host_routes', original_subnet['host_routes'])
-        if (segment_id and (host_routes != original_subnet['host_routes'] or
-                            gateway_ip != original_subnet['gateway_ip'])):
+        orig_segment_id = original_subnet.get('segment_id')
+        segment_id = subnet.get('segment_id', orig_segment_id)
+        orig_gateway_ip = original_subnet.get('gateway_ip')
+        gateway_ip = subnet.get('gateway_ip', orig_gateway_ip)
+        orig_host_routes = original_subnet.get('host_routes')
+        host_routes = subnet.get('host_routes', orig_host_routes)
+        if (segment_id and (host_routes != orig_host_routes or
+                            gateway_ip != orig_gateway_ip)):
             calc_host_routes = self._calculate_routed_network_host_routes(
                 context=context,
                 ip_version=netaddr.IPNetwork(original_subnet['cidr']).version,
@@ -584,8 +587,8 @@ class SegmentHostRoutes(object):
                 segment_id=segment_id,
                 host_routes=copy.deepcopy(host_routes),
                 gateway_ip=gateway_ip,
-                old_gateway_ip=original_subnet['gateway_ip'] if (
-                        gateway_ip != original_subnet['gateway_ip']) else None)
+                old_gateway_ip=orig_gateway_ip if (
+                        gateway_ip != orig_gateway_ip) else None)
             if self._host_routes_need_update(host_routes, calc_host_routes):
                 subnet['host_routes'] = calc_host_routes
 
diff --git a/neutron/tests/unit/extensions/test_segment.py b/neutron/tests/unit/extensions/test_segment.py
index 7e967711dda..6fd3f1e51fc 100644
--- a/neutron/tests/unit/extensions/test_segment.py
+++ b/neutron/tests/unit/extensions/test_segment.py
@@ -1701,10 +1701,10 @@ class TestNovaSegmentNotifier(SegmentAwareIpamTestCase):
             total += int(netaddr.IPAddress(pool['end']) -
                          netaddr.IPAddress(pool['start'])) + 1
         if total:
-            if subnet['gateway_ip']:
+            if subnet.get('gateway_ip'):
                 total += 1
                 reserved += 1
-            if subnet['enable_dhcp']:
+            if subnet.get('enable_dhcp'):
                 reserved += 1
         return total, reserved