diff --git a/ModbusMaster.cpp b/ModbusMaster.cpp
index 70fe245..419e8f0 100644
--- a/ModbusMaster.cpp
+++ b/ModbusMaster.cpp
@@ -33,12 +33,12 @@ Arduino library for communicating with Modbus slaves over RS232/485 (via RTU pro
 
 
 /* _____GLOBAL VARIABLES_____________________________________________________ */
-#ifdef __AVR__
+#if defined(ARDUINO_ARCH_AVR)
   HardwareSerial* MBSerial = &Serial; ///< Pointer to Serial class object
-#endif
-
-#ifdef __arm__
+#elif defined(ARDUINO_ARCH_SAM)
   UARTClass* MBSerial = &Serial; ///< Pointer to Serial class object
+#else
+  #error "This library only supports boards with an AVR or SAM processor. Please open an issue at https://github.com/4-20ma/ModbusMaster/issues and indicate which processor/platform you're using."
 #endif
 
 
diff --git a/library.properties b/library.properties
index 928713c..ec1edde 100644
--- a/library.properties
+++ b/library.properties
@@ -6,4 +6,4 @@ sentence=Enlighten your Arduino to be a Modbus master.
 paragraph=Enables communication with Modbus slaves over RS232/485 (via RTU protocol). Requires a RS232/485 transceiver.
 category=Communication
 url=https://github.com/4-20ma/ModbusMaster
-architectures=*
+architectures=avr,sam