diff --git a/core/net/mac/mac.h b/core/net/mac/mac.h
index 49f615a18..f464d0bbb 100644
--- a/core/net/mac/mac.h
+++ b/core/net/mac/mac.h
@@ -28,7 +28,7 @@
  *
  * This file is part of the Contiki operating system.
  *
- * $Id: mac.h,v 1.12 2010/02/18 21:48:39 adamdunkels Exp $
+ * $Id: mac.h,v 1.13 2010/02/28 20:18:30 adamdunkels Exp $
  */
 
 /**
@@ -86,6 +86,9 @@ enum {
   /**< The MAC layer did not get an acknowledgement for the packet. */
   MAC_TX_NOACK,
 
+  /**< The MAC layer deferred the transmission for a later time. */
+  MAC_TX_DEFERRED,
+
   /**< The MAC layer transmission could not be performed because of an
      error. The upper layer may try again later. */
   MAC_TX_ERR,