diff --git a/hardware/arduino/avr/libraries/SoftwareSerial/src/SoftwareSerial.h b/hardware/arduino/avr/libraries/SoftwareSerial/src/SoftwareSerial.h
index 26183ba85..b1a37c4ad 100644
--- a/hardware/arduino/avr/libraries/SoftwareSerial/src/SoftwareSerial.h
+++ b/hardware/arduino/avr/libraries/SoftwareSerial/src/SoftwareSerial.h
@@ -39,7 +39,10 @@ http://arduiniana.org.
 * Definitions
 ******************************************************************************/
 
+#ifndef _SS_MAX_RX_BUFF
 #define _SS_MAX_RX_BUFF 64 // RX buffer size
+#endif
+
 #ifndef GCC_VERSION
 #define GCC_VERSION (__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__)
 #endif