diff --git a/RFM69.cpp b/RFM69.cpp
index c7aefbf..81cf4e6 100644
--- a/RFM69.cpp
+++ b/RFM69.cpp
@@ -268,6 +268,7 @@ void RFM69::sendACK(const void* buffer, uint8_t bufferSize) {
   writeReg(REG_PACKETCONFIG2, (readReg(REG_PACKETCONFIG2) & 0xFB) | RF_PACKET2_RXRESTART); // avoid RX deadlocks
   uint32_t now = millis();
   while (!canSend() && millis() - now < RF69_CSMA_LIMIT_MS) receiveDone();
+  SENDERID = sender;    // TWS: Restore SenderID after it gets wiped out by receiveDone()
   sendFrame(sender, buffer, bufferSize, false, true);
   RSSI = _RSSI; // restore payload RSSI
 }
@@ -439,9 +440,11 @@ void RFM69::writeReg(uint8_t addr, uint8_t value)
 // select the RFM69 transceiver (save SPI settings, set CS low)
 void RFM69::select() {
   noInterrupts();
+#if defined (SPCR) && defined (SPSR)
   // save current SPI settings
   _SPCR = SPCR;
   _SPSR = SPSR;
+#endif
   // set RFM69 SPI settings
   SPI.setDataMode(SPI_MODE0);
   SPI.setBitOrder(MSBFIRST);
@@ -453,8 +456,10 @@ void RFM69::select() {
 void RFM69::unselect() {
   digitalWrite(_slaveSelectPin, HIGH);
   // restore SPI settings to what they were before talking to RFM69
+#if defined (SPCR) && defined (SPSR)
   SPCR = _SPCR;
   SPSR = _SPSR;
+#endif
   interrupts();
 }
 
diff --git a/RFM69.h b/RFM69.h
index 009d815..d90cab4 100644
--- a/RFM69.h
+++ b/RFM69.h
@@ -138,8 +138,10 @@ class RFM69 {
     bool _promiscuousMode;
     uint8_t _powerLevel;
     bool _isRFM69HW;
+#if defined (SPCR) && defined (SPSR)
     uint8_t _SPCR;
     uint8_t _SPSR;
+#endif
 
     virtual void receiveBegin();
     virtual void setMode(uint8_t mode);
diff --git a/RFM69_ATC.cpp b/RFM69_ATC.cpp
index ce556db..79c4bb9 100644
--- a/RFM69_ATC.cpp
+++ b/RFM69_ATC.cpp
@@ -232,14 +232,14 @@ void RFM69_ATC::receiveBegin() {
 // enableAutoPower() - call with target RSSI, use 0 to disable (default), any other value with turn on autotransmit control.
 //=============================================================================
 // TomWS1: New methods to address autoPower control
-void  RFM69_ATC::enableAutoPower(int targetRSSI){    // TomWS1: New method to enable/disable auto Power control
+void  RFM69_ATC::enableAutoPower(int16_t targetRSSI){    // TomWS1: New method to enable/disable auto Power control
   _targetRSSI = targetRSSI;         // no logic here, just set the value (if non-zero, then enabled), caller's responsibility to use a reasonable value
 }
 
 //=============================================================================
 // getAckRSSI() - returns the RSSI value ack'd by the far end.
 //=============================================================================
-int  RFM69_ATC::getAckRSSI(void){                     // TomWS1: New method to retrieve the ack'd RSSI (if any)
+int16_t  RFM69_ATC::getAckRSSI(void){                     // TomWS1: New method to retrieve the ack'd RSSI (if any)
   return (_targetRSSI==0?0:_ackRSSI);
 }
 
diff --git a/RFM69_ATC.h b/RFM69_ATC.h
index d4b677f..a57b45f 100644
--- a/RFM69_ATC.h
+++ b/RFM69_ATC.h
@@ -47,7 +47,7 @@ class RFM69_ATC: public RFM69 {
     void sendACK(const void* buffer = "", uint8_t bufferSize=0);
     //void setHighPower(bool onOFF=true, uint8_t PA_ctl=0x60); //have to call it after initialize for RFM69HW
     //void setPowerLevel(uint8_t level); // reduce/increase transmit power level
-    void  enableAutoPower(int targetRSSI=-90);  // TWS: New method to enable/disable auto Power control
+    void  enableAutoPower(int16_t targetRSSI=-90);  // TWS: New method to enable/disable auto Power control
     void setMode(uint8_t mode);  // TWS: moved from protected to try to build block()/unblock() wrapper
     
     int16_t getAckRSSI(void);       // TWS: New method to retrieve the ack'd RSSI (if any)
@@ -58,7 +58,7 @@ class RFM69_ATC: public RFM69 {
   protected:
     void interruptHook(uint8_t CTLbyte);
     void sendFrame(uint8_t toAddress, const void* buffer, uint8_t size, bool requestACK=false, bool sendACK=false);  // Need this one to match the RFM69 prototype.
-    void sendFrame(uint8_t toAddress, const void* buffer, uint8_t size, bool requestACK, bool sendACK, bool sendRSSI, int lastRSSI);
+    void sendFrame(uint8_t toAddress, const void* buffer, uint8_t size, bool requestACK, bool sendACK, bool sendRSSI, int16_t lastRSSI);
     void receiveBegin();
     //void setHighPowerRegs(bool onOff);