diff --git a/PN532.cpp b/PN532.cpp
index 122f414..a2fe42f 100644
--- a/PN532.cpp
+++ b/PN532.cpp
@@ -564,7 +564,7 @@ uint8_t PN532::mifareclassic_WriteNDEFURI (uint8_t sectorNumber, uint8_t uriIden
     // in NDEF records
 
     // Setup the sector buffer (w/pre-formatted TLV wrapper and NDEF message)
-    uint8_t sectorbuffer1[16] = {0x00, 0x00, 0x03, len + 5, 0xD1, 0x01, len + 1, 0x55, uriIdentifier, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+    uint8_t sectorbuffer1[16] = {0x00, 0x00, 0x03, (uint8_t)(len + 5U), 0xD1, 0x01, (uint8_t)(len + 1U), 0x55, uriIdentifier, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
     uint8_t sectorbuffer2[16] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
     uint8_t sectorbuffer3[16] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
     uint8_t sectorbuffer4[16] = {0xD3, 0xF7, 0xD3, 0xF7, 0xD3, 0xF7, 0x7F, 0x07, 0x88, 0x40, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};