diff --git a/src/MFRC522_I2C.cpp b/src/MFRC522_I2C.cpp
index 7baa85d..79ec8d1 100644
--- a/src/MFRC522_I2C.cpp
+++ b/src/MFRC522_I2C.cpp
@@ -815,7 +815,7 @@ byte MFRC522::PCD_Authenticate(byte command,		///< PICC_CMD_MF_AUTH_KEY_A or PIC
 	for (byte i = 0; i < MF_KEY_SIZE; i++) {	// 6 key bytes
 		sendData[2+i] = key->keyByte[i];
 	}
-	for (byte i = 0; i < 4; i++) {				// The first 4 bytes of the UID
+	for (byte i = 0; i < 4; i++) {				// The last 4 bytes of the UID
 		sendData[8+i] = uid->uidByte[i+uid->size-4];
 	}