diff --git a/crypto/rsa/rsa_oaep.c b/crypto/rsa/rsa_oaep.c
index 4f0bbab38..742b3a1c9 100644
--- a/crypto/rsa/rsa_oaep.c
+++ b/crypto/rsa/rsa_oaep.c
@@ -178,8 +178,10 @@ int MGF1(unsigned char *mask, long len, unsigned char *seed, long seedlen)
 
 	for (i = 0; outlen < len; i++)
 		{
-		cnt[0] = (i >> 24) & 255, cnt[1] = (i >> 16) & 255,
-			cnt[2] = (i >> 8) & 255, cnt[3] = i & 255;
+		cnt[0] = (unsigned char)((i >> 24) & 255);
+		cnt[1] = (unsigned char)((i >> 16) & 255);
+		cnt[2] = (unsigned char)((i >> 8)) & 255;
+		cnt[3] = (unsigned char)(i & 255);
 		SHA1_Init(&c);
 		SHA1_Update(&c, seed, seedlen);
 		SHA1_Update(&c, cnt, 4);