diff --git a/src/Cedar/Hub.c b/src/Cedar/Hub.c
index 0a37f8e0..184f3312 100644
--- a/src/Cedar/Hub.c
+++ b/src/Cedar/Hub.c
@@ -1563,13 +1563,15 @@ void HubWatchDogThread(THREAD *t, void *param)
 		o2 = NewListFast(NULL);
 
 		// Send an ARP packet
-		LockList(hub->IpTable);
+		LockHashList(hub->MacHashTable);
 		{
 			num = LIST_NUM(hub->IpTable);
 			for (i = 0;i < LIST_NUM(hub->IpTable);i++)
 			{
 				IP_TABLE_ENTRY *e = LIST_DATA(hub->IpTable, i);
 
+				if (e == NULL) continue;
+
 				if ((e->UpdatedTime + (UINT64)(IP_TABLE_EXPIRE_TIME)) > Tick64())
 				{
 					if (e->MacAddress[0] != 0xff || e->MacAddress[1] != 0xff || e->MacAddress[2] != 0xff ||
@@ -1645,7 +1647,7 @@ void HubWatchDogThread(THREAD *t, void *param)
 				}
 			}
 		}
-		UnlockList(hub->IpTable);
+		UnlockHashList(hub->MacHashTable);
 
 		if ((LIST_NUM(o) + LIST_NUM(o2)) != 0)
 		{