diff --git a/arch/cpu/cc2538/dev/gpio-hal-arch.h b/arch/cpu/cc2538/dev/gpio-hal-arch.h
index 0b282c738..25abb3eb4 100644
--- a/arch/cpu/cc2538/dev/gpio-hal-arch.h
+++ b/arch/cpu/cc2538/dev/gpio-hal-arch.h
@@ -53,6 +53,7 @@
 #include <stdint.h>
 /*---------------------------------------------------------------------------*/
 #define PIN_TO_PORT(pin) (pin >> 3)
+#define PIN_TO_NUM(pin) (pin % 8)
 #define PIN_TO_PORT_BASE(pin) GPIO_PORT_TO_BASE(PIN_TO_PORT(pin))
 /*---------------------------------------------------------------------------*/
 #define gpio_hal_arch_interrupt_enable(p) do { \
diff --git a/os/dev/gpio-hal.h b/os/dev/gpio-hal.h
index aacbfb1f1..b6af7bf74 100644
--- a/os/dev/gpio-hal.h
+++ b/os/dev/gpio-hal.h
@@ -130,6 +130,13 @@ typedef struct gpio_hal_event_handler_s {
   gpio_hal_pin_mask_t pin_mask;
 } gpio_hal_event_handler_t;
 /*---------------------------------------------------------------------------*/
+/**
+ * \brief Unknown GPIO
+ *
+ * A default GPIO value for unknown GPIO
+ */
+#define GPIO_HAL_PIN_UNKNOWN              0xFF
+/*---------------------------------------------------------------------------*/
 /**
  * \name Core GPIO functions
  *