diff --git a/core/net/mac/nullrdc.c b/core/net/mac/nullrdc.c
index ff367cf63..6d4117953 100644
--- a/core/net/mac/nullrdc.c
+++ b/core/net/mac/nullrdc.c
@@ -45,6 +45,10 @@
 #include "net/rime/rimestats.h"
 #include <string.h>
 
+#if CONTIKI_TARGET_COOJA
+#include "lib/simEnvChange.h"
+#endif /* CONTIKI_TARGET_COOJA */
+
 #define DEBUG 0
 #if DEBUG
 #include <stdio.h>
@@ -172,7 +176,12 @@ send_one_packet(mac_callback_t sent, void *ptr)
           /* Check for ack */
           wt = RTIMER_NOW();
           watchdog_periodic();
-          while(RTIMER_CLOCK_LT(RTIMER_NOW(), wt + ACK_WAIT_TIME));
+          while(RTIMER_CLOCK_LT(RTIMER_NOW(), wt + ACK_WAIT_TIME)) {
+#if CONTIKI_TARGET_COOJA
+            simProcessRunValue = 1;
+            cooja_mt_yield();
+#endif /* CONTIKI_TARGET_COOJA */
+          }
 
           ret = MAC_TX_NOACK;
           if(NETSTACK_RADIO.receiving_packet() ||
@@ -181,10 +190,17 @@ send_one_packet(mac_callback_t sent, void *ptr)
             int len;
             uint8_t ackbuf[ACK_LEN];
 
-            wt = RTIMER_NOW();
-            watchdog_periodic();
-            while(RTIMER_CLOCK_LT(RTIMER_NOW(),
-                                  wt + AFTER_ACK_DETECTED_WAIT_TIME));
+            if(AFTER_ACK_DETECTED_WAIT_TIME > 0) {
+              wt = RTIMER_NOW();
+              watchdog_periodic();
+              while(RTIMER_CLOCK_LT(RTIMER_NOW(),
+                                    wt + AFTER_ACK_DETECTED_WAIT_TIME)) {
+      #if CONTIKI_TARGET_COOJA
+                  simProcessRunValue = 1;
+                  cooja_mt_yield();
+      #endif /* CONTIKI_TARGET_COOJA */
+              }
+            }
 
             if(NETSTACK_RADIO.pending_packet()) {
               len = NETSTACK_RADIO.read(ackbuf, ACK_LEN);
diff --git a/platform/cooja/contiki-conf.h b/platform/cooja/contiki-conf.h
index f3580327b..51ff18bfb 100644
--- a/platform/cooja/contiki-conf.h
+++ b/platform/cooja/contiki-conf.h
@@ -65,10 +65,10 @@
 /* Default network config */
 #if WITH_UIP6
 
-#define NULLRDC_CONF_802154_AUTOACK  0
-#define NULLRDC_CONF_SEND_802154_ACK 0
+#define NULLRDC_CONF_802154_AUTOACK  1
+#define NULLRDC_CONF_SEND_802154_ACK 1
 #define NULLRDC_CONF_ACK_WAIT_TIME                RTIMER_SECOND / 500
-#define NULLRDC_CONF_AFTER_ACK_DETECTED_WAIT_TIME RTIMER_SECOND / 250
+#define NULLRDC_CONF_AFTER_ACK_DETECTED_WAIT_TIME 0
 
 
 /* Network setup for IPv6 */
diff --git a/platform/cooja/dev/cooja-radio.c b/platform/cooja/dev/cooja-radio.c
index e7cdce6dd..d30bf61c6 100644
--- a/platform/cooja/dev/cooja-radio.c
+++ b/platform/cooja/dev/cooja-radio.c
@@ -162,10 +162,14 @@ radio_send(const void *payload, unsigned short payload_len)
 {
   int radiostate = simRadioHWOn;
 
-  /* Simulate turnaround time of 1ms */
+  /* Simulate turnaround time of 2ms for packets, 1ms for acks*/
 #if WITH_TURNAROUND
   simProcessRunValue = 1;
   cooja_mt_yield();
+  if(payload_len > 3) {
+    simProcessRunValue = 1;
+    cooja_mt_yield();
+  }
 #endif /* WITH_TURNAROUND */
 
   if(!simRadioHWOn) {