diff --git a/core/net/mac/contikimac/contikimac.c b/core/net/mac/contikimac/contikimac.c
index 7912fe7dd..3c3e76429 100644
--- a/core/net/mac/contikimac/contikimac.c
+++ b/core/net/mac/contikimac/contikimac.c
@@ -502,10 +502,9 @@ powercycle(struct rtimer *t, void *ptr)
       ensure an occasional wake cycle or foreground processing will
       be blocked until a packet is detected */
 #if RDC_CONF_MCU_SLEEP
-
       static uint8_t sleepcycle;
-      if((sleepcycle++ < mcusleepcycle) && !we_are_sending && !radio_is_on) {
-        rtimer_arch_sleep(RTIMER_NOW() - cycle_start);
+      if((sleepcycle++ < mcusleepcycle) && !we_are_sending && !radio_is_on && !(NETSTACK_RADIO.receiving_packet() || NETSTACK_RADIO.pending_packet())) {
+          rtimer_arch_sleep(cycle_start - RTIMER_NOW());
       } else {
         sleepcycle = 0;
 #ifndef RDC_CONF_PT_YIELD_OFF
diff --git a/cpu/avr/radio/rf230bb/rf230bb.c b/cpu/avr/radio/rf230bb/rf230bb.c
index 624018f36..6f5c5e47d 100644
--- a/cpu/avr/radio/rf230bb/rf230bb.c
+++ b/cpu/avr/radio/rf230bb/rf230bb.c
@@ -1796,8 +1796,8 @@ rf230_cca(void)
 // if (cca & 0x40) {/*DEBUGFLOW('3')*/;} else {rf230_pending=1;DEBUGFLOW('4');}  
    if (cca & 0x40) {
 //   DEBUGFLOW('5');
-//	 return 1;
-         return 0;
+	 return 1;
+//     return 0;
    } else {
 //  DEBUGFLOW('6');
  busyexit: