diff --git a/at.py b/at.py
index 6839c60..1fd0b5c 100644
--- a/at.py
+++ b/at.py
@@ -136,10 +136,11 @@ class Updater(threading.Thread):
         else:
             atime = time()
         self.lock.acquire()
-        self.active[hwaddr] = (atime, ip, name)
+        if hwaddr not in self.active or self.active[hwaddr][0] < atime:
+            self.active[hwaddr] = (atime, ip, name)
+            app.logger.info('updated %s with atime %s and ip %s',
+                            hwaddr, strfts(atime), ip)
         self.lock.release()
-        app.logger.info('updated %s with atime %s and ip %s',
-                        hwaddr, strfts(atime), ip)
 
 
 class CapUpdater(Updater):