diff --git a/core/net/mac/lpp.c b/core/net/mac/lpp.c
index 47b3cc201..52b71b55e 100644
--- a/core/net/mac/lpp.c
+++ b/core/net/mac/lpp.c
@@ -28,7 +28,7 @@
  *
  * This file is part of the Contiki operating system.
  *
- * $Id: lpp.c,v 1.28 2009/12/06 13:18:32 adamdunkels Exp $
+ * $Id: lpp.c,v 1.29 2010/01/25 11:43:32 adamdunkels Exp $
  */
 
 /**
@@ -882,6 +882,12 @@ off(int keep_radio_on)
   return 1;
 }
 /*---------------------------------------------------------------------------*/
+static unsigned short
+channel_check_interval(void)
+{
+  return OFF_TIME + LISTEN_TIME;
+}
+/*---------------------------------------------------------------------------*/
 const struct mac_driver lpp_driver = {
   "LPP",
   lpp_init,
@@ -890,6 +896,7 @@ const struct mac_driver lpp_driver = {
   set_receive_function,
   on,
   off,
+  channel_check_interval,
 };
 /*---------------------------------------------------------------------------*/
 static void
diff --git a/core/net/mac/mac.h b/core/net/mac/mac.h
index 06c5850eb..684290661 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 1.7 2009/12/05 21:49:51 adamdunkels Exp $
+ * $Id: mac.h,v 1.8 2010/01/25 11:43:32 adamdunkels Exp $
  */
 
 /**
@@ -66,6 +66,9 @@ struct mac_driver {
 
   /** Turn the MAC layer off. */
   int (* off)(int keep_radio_on);
+
+  /** Returns the channel check interval, expressed in clock_time_t ticks. */
+  unsigned short (* channel_check_interval)(void);
 };
 
 /* Generic MAC return values. */
diff --git a/core/net/mac/nullmac.c b/core/net/mac/nullmac.c
index 41daa45ed..02153f660 100644
--- a/core/net/mac/nullmac.c
+++ b/core/net/mac/nullmac.c
@@ -28,7 +28,7 @@
  *
  * This file is part of the Contiki operating system.
  *
- * $Id: nullmac.c,v 1.12 2009/12/05 13:29:41 adamdunkels Exp $
+ * $Id: nullmac.c,v 1.13 2010/01/25 11:43:32 adamdunkels Exp $
  */
 
 /**
@@ -93,6 +93,12 @@ off(int keep_radio_on)
   }
 }
 /*---------------------------------------------------------------------------*/
+static unsigned short
+channel_check_interval(void)
+{
+  return 0;
+}
+/*---------------------------------------------------------------------------*/
 const struct mac_driver nullmac_driver = {
   "nullmac",
   nullmac_init,
@@ -101,6 +107,7 @@ const struct mac_driver nullmac_driver = {
   set_receive_function,
   on,
   off,
+  channel_check_interval,
 };
 /*---------------------------------------------------------------------------*/
 const struct mac_driver *
diff --git a/core/net/mac/xmac.c b/core/net/mac/xmac.c
index b202d76c6..40c44be1e 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 1.48 2010/01/14 20:14:03 adamdunkels Exp $
+ * $Id: xmac.c,v 1.49 2010/01/25 11:43:32 adamdunkels Exp $
  */
 
 /**
@@ -920,6 +920,12 @@ turn_off(int keep_radio_on)
   }
 }
 /*---------------------------------------------------------------------------*/
+static unsigned short
+channel_check_interval(void)
+{
+  return (1ul * CLOCK_SECOND * DEFAULT_PERIOD) / RTIMER_ARCH_SECOND;
+}
+/*---------------------------------------------------------------------------*/
 const struct mac_driver xmac_driver =
   {
     "X-MAC",
@@ -928,5 +934,6 @@ const struct mac_driver xmac_driver =
     read_packet,
     set_receive_function,
     turn_on,
-    turn_off
+    turn_off,
+    channel_check_interval,
   };