Index: firmware/App/Services/MsgQueues.h
===================================================================
diff -u -r52863cba9685f31136ab3f4b4764a17ccf34fc05 -r9864b14f76782f1e68bf266dcd843451748715a0
--- firmware/App/Services/MsgQueues.h	(.../MsgQueues.h)	(revision 52863cba9685f31136ab3f4b4764a17ccf34fc05)
+++ firmware/App/Services/MsgQueues.h	(.../MsgQueues.h)	(revision 9864b14f76782f1e68bf266dcd843451748715a0)
@@ -32,6 +32,9 @@
 #pragma pack(push,1)
 typedef struct
 {
+#ifdef ACK_IMPLEMENTED
+    U16 seqNo;                                  // sequence # (and ACK required bit) of message
+#endif
     U16 msgID;                                  // ID of message
     U08 payloadLen;                             // length of payload in bytes
 } MESSAGE_HEADER_T;