diff --git a/sw/airborne/fms/fms_spi_link.c b/sw/airborne/fms/fms_spi_link.c
index 00991abfd9..860062bcbb 100644
--- a/sw/airborne/fms/fms_spi_link.c
+++ b/sw/airborne/fms/fms_spi_link.c
@@ -76,7 +76,7 @@ int spi_link_send(void *buf_out, size_t count, void *buf_in, uint8_t* crc_valid)
 #define TOPBIT (1 << (WIDTH - 1))
 uint8_t crc_calc_block_crc8(const uint8_t buf[], uint32_t len) {
   uint8_t  _remainder = 0;	
-  for (int byte = 0; byte < len; ++byte)  {
+  for (uint32_t byte = 0; byte < len; ++byte)  {
     _remainder ^= (buf[byte] << (WIDTH - 8));
     for (uint8_t bit = 8; bit > 0; --bit)  {
       if (_remainder & TOPBIT)