diff --git a/hardware/arduino/cores/arduino/HardwareSerial.cpp b/hardware/arduino/cores/arduino/HardwareSerial.cpp
index 1b1fa71d8..9985b78c6 100644
--- a/hardware/arduino/cores/arduino/HardwareSerial.cpp
+++ b/hardware/arduino/cores/arduino/HardwareSerial.cpp
@@ -46,8 +46,8 @@
 struct ring_buffer
 {
   unsigned char buffer[SERIAL_BUFFER_SIZE];
-  volatile int head;
-  volatile int tail;
+  volatile unsigned int head;
+  volatile unsigned int tail;
 };
 
 #if defined(USBCON)
diff --git a/libraries/SD/utility/SdFatUtil.h b/libraries/SD/utility/SdFatUtil.h
index 283fcb21a..7d6b4104f 100644
--- a/libraries/SD/utility/SdFatUtil.h
+++ b/libraries/SD/utility/SdFatUtil.h
@@ -56,7 +56,7 @@ static UNUSEDOK int FreeRam(void) {
  * \param[in] str Pointer to string stored in flash memory.
  */
 static NOINLINE void SerialPrint_P(PGM_P str) {
-  for (uint8_t c; (c = pgm_read_byte(str)); str++) Serial.print(c);
+  for (uint8_t c; (c = pgm_read_byte(str)); str++) Serial.write(c);
 }
 //------------------------------------------------------------------------------
 /**