diff --git a/src/MFRC522.h b/src/MFRC522.h
index 7fa6288..0aa9de8 100644
--- a/src/MFRC522.h
+++ b/src/MFRC522.h
@@ -142,6 +142,8 @@ class MFRC522 {
 public:
 	// Size of the MFRC522 FIFO
 	static const byte FIFO_SIZE = 64;		// The FIFO is 64 bytes.
+	// Default value for unused pin
+	static constexpr uint8_t UNUSED_PIN = UINT8_MAX;
 
 	// MFRC522 registers. Described in chapter 9 of the datasheet.
 	// When using SPI all addresses are shifted one bit left in the "SPI address byte" (section 8.1.2.3)