--- a/src/devices/wifi/mac-low.cc	Mon Dec 17 13:41:51 2007 +0100
+++ b/src/devices/wifi/mac-low.cc	Wed Dec 19 13:22:55 2007 +0100
@@ -230,7 +230,8 @@
     m_sendAckEvent (),
     m_sendDataEvent (),
     m_waitSifsEvent (),
-    m_currentPacket (0)
+    m_currentPacket (0),
+    m_listener (0)
 {
   m_lastNavDuration = Seconds (0);
   m_lastNavStart = Seconds (0);
@@ -294,6 +295,7 @@
   if (oneRunning && m_listener != 0) 
     {
       m_listener->Cancel ();
+      m_listener = 0;
     }
 }