diff --git a/tools/cooja/java/org/contikios/cooja/contikimote/interfaces/ContikiRadio.java b/tools/cooja/java/org/contikios/cooja/contikimote/interfaces/ContikiRadio.java
index 5502b9a8a..bbc4a2abd 100644
--- a/tools/cooja/java/org/contikios/cooja/contikimote/interfaces/ContikiRadio.java
+++ b/tools/cooja/java/org/contikios/cooja/contikimote/interfaces/ContikiRadio.java
@@ -48,7 +48,7 @@ import org.contikios.cooja.interfaces.Position;
 import org.contikios.cooja.interfaces.Radio;
 import org.contikios.cooja.mote.memory.VarMemory;
 import org.contikios.cooja.radiomediums.UDGM;
-
+import org.contikios.cooja.util.CCITT_CRC;
 /**
  * Packet radio transceiver mote interface.
  *
@@ -200,7 +200,7 @@ public class ContikiRadio extends Radio implements ContikiMoteInterface, PolledA
       packetToMote = null;
       myMoteMemory.setIntValueOf("simInSize", 0);
     } else {
-      myMoteMemory.setIntValueOf("simInSize", packetToMote.getPacketData().length);
+      myMoteMemory.setIntValueOf("simInSize", packetToMote.getPacketData().length - 2);
       myMoteMemory.setByteArray("simInDataBuffer", packetToMote.getPacketData());
     }
 
@@ -330,7 +330,7 @@ public class ContikiRadio extends Radio implements ContikiMoteInterface, PolledA
     /* New transmission */
     int size = myMoteMemory.getIntValueOf("simOutSize");
     if (!isTransmitting && size > 0) {
-      packetFromMote = new COOJARadioPacket(myMoteMemory.getByteArray("simOutDataBuffer", size));
+      packetFromMote = new COOJARadioPacket(myMoteMemory.getByteArray("simOutDataBuffer", size + 2));
 
       if (packetFromMote.getPacketData() == null || packetFromMote.getPacketData().length == 0) {
         logger.warn("Skipping zero sized Contiki packet (no buffer)");
@@ -339,6 +339,15 @@ public class ContikiRadio extends Radio implements ContikiMoteInterface, PolledA
         return;
       }
 
+      byte[] data = packetFromMote.getPacketData();
+      CCITT_CRC txCrc = new CCITT_CRC();
+      txCrc.setCRC(0);
+      for (int i = 0; i < size; i++) {
+        txCrc.addBitrev(data[i]);
+      }
+      data[size] = (byte)txCrc.getCRCHi();
+      data[size + 1] = (byte)txCrc.getCRCLow();
+
       isTransmitting = true;
 
       /* Calculate transmission duration (us) */
diff --git a/tools/cooja/java/org/contikios/cooja/util/CCITT_CRC.java b/tools/cooja/java/org/contikios/cooja/util/CCITT_CRC.java
new file mode 100644
index 000000000..ea991208b
--- /dev/null
+++ b/tools/cooja/java/org/contikios/cooja/util/CCITT_CRC.java
@@ -0,0 +1,89 @@
+/**
+ * Copyright (c) 2008, Swedish Institute of Computer Science.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the Institute nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * This file is part of MSPSim.
+ *
+ * -----------------------------------------------------------------
+ *
+ * Author  : Joakim Eriksson
+ */
+
+package org.contikios.cooja.util;
+
+/* basic CRC-CCITT code */
+public class CCITT_CRC {
+  int crc;
+
+  public int getCRC() {
+    return crc;
+  }
+
+  /* this will only work with zero... */
+  public void setCRC(int val) {
+    crc = val;
+  }
+  
+  public void clr() {
+    crc = 0xffff;
+  }
+
+  public void addBitrev(int data) {
+      add(bitrev(data));
+  }
+  
+  public int getCRCLow() {
+      return bitrev(crc & 0xff);
+  }
+
+  public int getCRCHi() {
+      return bitrev(crc >> 8);
+  }
+
+  
+  public int add(int data) {
+    int newCrc = ((crc >> 8) & 0xff) | (crc << 8) & 0xffff;
+    newCrc ^= (data & 0xff);
+    newCrc ^= (newCrc & 0xff) >> 4;
+    newCrc ^= (newCrc << 12) & 0xffff;
+    newCrc ^= (newCrc & 0xff) << 5;
+    crc = newCrc & 0xffff;
+    return crc;
+  }
+
+  public int getCRCBitrev() {
+      return getCRCLow() + (getCRCHi() << 8);
+  }
+  
+  public static final String hex = "0123456789abcdef";
+
+  private static int bitrev(int data) {
+      return ((data << 7) & 0x80) | ((data << 5) & 0x40) |
+      (data << 3) & 0x20 | (data << 1) & 0x10 |
+      (data >> 7) & 0x01 | (data >> 5) & 0x02 |
+      (data >> 3) & 0x04 | (data >> 1) & 0x08;
+  }
+}