diff --git a/core/net/mac/xmac.c b/core/net/mac/xmac.c
index c704607c3..7d9d2d969 100644
--- a/core/net/mac/xmac.c
+++ b/core/net/mac/xmac.c
@@ -28,7 +28,7 @@
  *
  * This file is part of the Contiki operating system.
  *
- * $Id: xmac.c,v 1.28 2009/03/12 21:58:20 adamdunkels Exp $
+ * $Id: xmac.c,v 1.29 2009/03/23 21:00:25 adamdunkels Exp $
  */
 
 /**
@@ -342,8 +342,12 @@ format_announcement(char *hdr)
     adata->num++;
   }
 
-  return ANNOUNCEMENT_MSG_HEADERLEN +
-    sizeof(struct announcement_data) * adata->num;
+  if(adata->num > 0) {
+    return ANNOUNCEMENT_MSG_HEADERLEN +
+      sizeof(struct announcement_data) * adata->num;
+  } else {
+    return 0;
+  }
 }
 #endif /* XMAC_CONF_ANNOUNCEMENTS */
 /*---------------------------------------------------------------------------*/
@@ -698,10 +702,10 @@ send_announcement(void *ptr)
   announcement_len = format_announcement((char *)hdr +
 					 sizeof(struct xmac_hdr));
 
-  packetbuf_set_datalen(sizeof(struct xmac_hdr) + announcement_len);
-
-  /*  PRINTF("Sending probe\n");*/
-  radio->send(packetbuf_hdrptr(), packetbuf_totlen());
+  if(announcement_len > 0) {
+    packetbuf_set_datalen(sizeof(struct xmac_hdr) + announcement_len);
+    radio->send(packetbuf_hdrptr(), packetbuf_totlen());
+  }
 }
 /*---------------------------------------------------------------------------*/
 static void