diff --git a/mxssb.c b/mxssb.c
index cb8fe896ce0d0f2d42fd03827b21f3c599d905bb..b2f8b1fce5d3f4fe174c714b4f3070c39e174da7 100644
--- a/mxssb.c
+++ b/mxssb.c
@@ -174,17 +174,17 @@ static int sb_aes_reinit(struct sb_image_ctx *ictx, int enc)
 /*
  * CRC32
  */
-static uint32_t crc32(uint8_t *data, int len)
+static uint32_t crc32(uint8_t *data, uint32_t len)
 {
 	const uint32_t poly = 0x04c11db7;
 	uint32_t crc32 = 0xffffffff;
-	int byte, bit;
+	unsigned int byte, bit;
 
 	for (byte = 0; byte < len; byte++) {
 		crc32 ^= data[byte] << 24;
 
 		for (bit = 8; bit > 0; bit--) {
-			if (crc32 & (1 << 31))
+			if (crc32 & (1UL << 31))
 				crc32 = (crc32 << 1) ^ poly;
 			else
 				crc32 = (crc32 << 1);