diff --git a/SPP.cpp b/SPP.cpp
index 0c133830..f0a83927 100644
--- a/SPP.cpp
+++ b/SPP.cpp
@@ -756,17 +756,29 @@ bool SPP::checkFcs(uint8_t *data, uint8_t fcs) {
 }
 
 /* Serial commands */
+#if defined(ARDUINO) && ARDUINO >=100
 size_t SPP::write(uint8_t data) {
-        return write(&data,1);
+        return write(&data, 1);
 }
+#else
+void SPP::write(uint8_t data) {
+        write(&data, 1);
+}
+#endif
 
+#if defined(ARDUINO) && ARDUINO >=100
 size_t SPP::write(const uint8_t *data, size_t size) {
+#else
+void SPP::write(const uint8_t *data, size_t size) {
+#endif
         for(uint8_t i = 0; i < size; i++) {
                 if(sppIndex >= sizeof(sppOutputBuffer)/sizeof(sppOutputBuffer[0]))
                         send(); // Send the current data in the buffer
                 sppOutputBuffer[sppIndex++] = data[i]; // All the bytes are put into a buffer and then send using the send() function
         }
+#if defined(ARDUINO) && ARDUINO >=100
         return size;
+#endif
 }
 
 void SPP::send() {
diff --git a/SPP.h b/SPP.h
index 81b83829..201fb77b 100644
--- a/SPP.h
+++ b/SPP.h
@@ -147,6 +147,8 @@ public:
          * @return Return the byte. Will return -1 if no bytes are available.
          */
         virtual int read(void);
+
+#if defined(ARDUINO) && ARDUINO >=100
         /**
          * Writes the byte to send to a buffer. The message is send when either send() or after Usb.Task() is called.
          * @param  data The byte to write.
@@ -162,6 +164,20 @@ public:
         virtual size_t write(const uint8_t* data, size_t size);
         /** Pull in write(const char *str) from Print */
         using Print::write;
+#else
+        /**
+         * Writes the byte to send to a buffer. The message is send when either send() or after Usb.Task() is called.
+         * @param  data The byte to write.
+         */
+        virtual void write(uint8_t data);
+        /**
+         * Writes the bytes to send to a buffer. The message is send when either send() or after Usb.Task() is called.
+         * @param data The data array to send.
+         * @param size Size of the data.
+         */
+        virtual void write(const uint8_t* data, size_t size);
+#endif
+
         /** Discard all the bytes in the buffer. */
         void discard(void);
         /**
diff --git a/settings.h b/settings.h
index bd64ff3f..bc8878ee 100644
--- a/settings.h
+++ b/settings.h
@@ -75,6 +75,7 @@
 #include <pins_arduino.h>
 #include <avr/pgmspace.h>
 #include <avr/io.h>
+#define F(str) (str)
 #endif
 
 #if USE_XMEM_SPI_LOCK | defined(USE_MULTIPLE_APP_API)