diff --git a/cores/arduino/pins_arduino.c b/cores/arduino/pins_arduino.c
index 70c8d0556c..eeebdd8e15 100644
--- a/cores/arduino/pins_arduino.c
+++ b/cores/arduino/pins_arduino.c
@@ -26,10 +26,12 @@ void __libc_init_array(void);
 
 WEAK uint32_t pinNametoDigitalPin(PinName p)
 {
-  uint32_t i = 0;
-  for(i = 0; i < NUM_DIGITAL_PINS; i++) {
-	  if (digitalPin[i] == p)
-		  break;
+  uint32_t i = NC;
+  if(STM_VALID_PINNAME(p)) {
+    for(i = 0; i < NUM_DIGITAL_PINS; i++) {
+      if (digitalPin[i] == p)
+        break;
+    }
   }
   return i;
 }
diff --git a/cores/arduino/pins_arduino.h b/cores/arduino/pins_arduino.h
index d43b24394a..203b38febd 100644
--- a/cores/arduino/pins_arduino.h
+++ b/cores/arduino/pins_arduino.h
@@ -32,38 +32,51 @@ extern "C" {
 #    include <syscalls.h> /** RedHat Newlib minimal stub */
 #endif
 
-#define NOT_AN_INTERRUPT        NC // -1
+#define NOT_AN_INTERRUPT            NC // -1
 
-#define NUM_DIGITAL_PINS        DEND
-#define NUM_ANALOG_INPUTS       (AEND-A0)
+#define NUM_DIGITAL_PINS            DEND
+#define NUM_ANALOG_INPUTS           (AEND-A0)
 
 // Convert a digital pin number Dxx to a PinName Pxy
 // Note: Analog pin is also a digital pin.
-#define digitalPinToPinName(p)     ((p < NUM_DIGITAL_PINS) ? digitalPin[p] : (STM_VALID_PINNAME(p))? (PinName)p : NC)
+#define digitalPinToPinName(p)      ((p < NUM_DIGITAL_PINS) ? digitalPin[p] : NC)
 // Convert a PinName Pxy to a digital pin number
 uint32_t pinNametoDigitalPin(PinName p);
 
 // Convert an analog pin number to a digital pin number
 // Used by analogRead api to have A0 == 0
-#define analogInputToDigitalPin(p) ((p < NUM_ANALOG_INPUTS) ? (p+A0) : p)
+#define analogInputToDigitalPin(p)  ((p < NUM_ANALOG_INPUTS) ? (p+A0) : p)
 // Convert an analog pin number Axx to a PinName Pxy
-#define analogInputToPinName(p)    (digitalPinToPinName(analogInputToDigitalPin(p)))
+#define analogInputToPinName(p)     (digitalPinToPinName(analogInputToDigitalPin(p)))
 // All pins could manage EXTI
-#define digitalPinToInterrupt(p)   ((p>=D0) && (p < NUM_DIGITAL_PINS) ? p : NOT_AN_INTERRUPT)
+#define digitalPinToInterrupt(p)    ((digitalPinIsValid(p) ? p : NOT_AN_INTERRUPT)
 
-#define digitalPinHasI2C(p)        (pin_in_pinmap(digitalPinToPinName(p), PinMap_I2C_SDA) ||\
-                                    pin_in_pinmap(digitalPinToPinName(p), PinMap_I2C_SCL))
-#define digitalPinHasPWM(p)        (pin_in_pinmap(digitalPinToPinName(p), PinMap_PWM))
-#define digitalPinHasSerial(p)     (pin_in_pinmap(digitalPinToPinName(p), PinMap_UART_RX) ||\
-                                    pin_in_pinmap(digitalPinToPinName(p), PinMap_UART_TX))
-#define digitalPinHasSPI(p)        (pin_in_pinmap(digitalPinToPinName(p), PinMap_SPI_MOSI) ||\
-                                    pin_in_pinmap(digitalPinToPinName(p), PinMap_SPI_MISO) ||\
-                                    pin_in_pinmap(digitalPinToPinName(p), PinMap_SPI_SCLK) ||\
-                                    pin_in_pinmap(digitalPinToPinName(p), PinMap_SPI_SSEL))
+#define digitalPinHasI2C(p)         (pin_in_pinmap(digitalPinToPinName(p), PinMap_I2C_SDA) ||\
+                                     pin_in_pinmap(digitalPinToPinName(p), PinMap_I2C_SCL))
+#define digitalPinHasPWM(p)         (pin_in_pinmap(digitalPinToPinName(p), PinMap_PWM))
+#define digitalPinHasSerial(p)      (pin_in_pinmap(digitalPinToPinName(p), PinMap_UART_RX) ||\
+                                     pin_in_pinmap(digitalPinToPinName(p), PinMap_UART_TX))
+#define digitalPinHasSPI(p)         (pin_in_pinmap(digitalPinToPinName(p), PinMap_SPI_MOSI) ||\
+                                     pin_in_pinmap(digitalPinToPinName(p), PinMap_SPI_MISO) ||\
+                                     pin_in_pinmap(digitalPinToPinName(p), PinMap_SPI_SCLK) ||\
+                                     pin_in_pinmap(digitalPinToPinName(p), PinMap_SPI_SSEL))
 
 
-#define digitalPinToPort(p)        ( get_GPIO_Port(digitalPinToPinName(p)) )
-#define digitalPinToBitMask(p)     ( STM_GPIO_PIN(digitalPinToPinName(p)) )
+#define digitalPinToPort(p)         (get_GPIO_Port(digitalPinToPinName(p)))
+#define digitalPinToBitMask(p)      (STM_GPIO_PIN(digitalPinToPinName(p)))
+
+#define digitalPinIsValid(p)        (digitalPinToPinName(p) != NC)
+
+// As some pin could be duplicated in digitalPin[]
+// return first occurence of linked PinName (PYx)
+#define digitalPinFirstOccurence(p) (pinNametoDigitalPin(digitalPinToPinName(p)))
+
+// Specific for Firmata. As some pins could be duplicated,
+// ensure 'p' is not one of the serial pins
+#if defined(PIN_SERIAL_RX) && defined(PIN_SERIAL_TX)
+#define pinIsSerial(p)              ((digitalPinFirstOccurence(p) == PIN_SERIAL_RX) ||\
+                                     (digitalPinFirstOccurence(p) == PIN_SERIAL_TX))
+#endif
 
 #ifdef __cplusplus
 }
diff --git a/libraries/Firmata/Boards.h b/libraries/Firmata/Boards.h
index 82e6c725cf..5f1278035c 100644
--- a/libraries/Firmata/Boards.h
+++ b/libraries/Firmata/Boards.h
@@ -771,14 +771,14 @@ writePort(port, value, bitmask):  Write an 8 bit port.
 #define TOTAL_PORTS             MAX_NB_PORT
 #define VERSION_BLINK_PIN       LED_BUILTIN
 // PIN_SERIALY_RX/TX defined in the variant.h
-#define IS_PIN_DIGITAL(p)       ((p != PIN_SERIAL_RX) && (p != PIN_SERIAL_TX) && (p < TOTAL_PINS))
-#define IS_PIN_ANALOG(p)        ((p) >= A0 && (p) < AEND)
-#define IS_PIN_PWM(p)           digitalPinHasPWM(p)
+#define IS_PIN_DIGITAL(p)       (digitalPinIsValid(p) && !pinIsSerial(p))
+#define IS_PIN_ANALOG(p)        ((p >= A0) && (p < AEND) && !pinIsSerial(p))
+#define IS_PIN_PWM(p)           (IS_PIN_DIGITAL(p) && digitalPinHasPWM(p))
 #define IS_PIN_SERVO(p)         IS_PIN_DIGITAL(p)
-#define IS_PIN_I2C(p)           digitalPinHasI2C(p)
-#define IS_PIN_SPI(p)           digitalPinHasSPI(p)
-#define IS_PIN_INTERRUPT(p)     (digitalPinToInterrupt(p) > NOT_AN_INTERRUPT)
-#define IS_PIN_SERIAL(p)        digitalPinHasSerial(p)
+#define IS_PIN_I2C(p)           (IS_PIN_DIGITAL(p) && digitalPinHasI2C(p))
+#define IS_PIN_SPI(p)           (IS_PIN_DIGITAL(p) && digitalPinHasSPI(p))
+#define IS_PIN_INTERRUPT(p)     (IS_PIN_DIGITAL(p) && (digitalPinToInterrupt(p) > NOT_AN_INTERRUPT)))
+#define IS_PIN_SERIAL(p)        (digitalPinHasSerial(p))
 #define PIN_TO_DIGITAL(p)       (p)
 #define PIN_TO_ANALOG(p)        (p-A0)
 #define PIN_TO_PWM(p)           (p)