diff --git a/src/libopensc/card-flex.c b/src/libopensc/card-flex.c
index 3c031285..00d6eb62 100644
--- a/src/libopensc/card-flex.c
+++ b/src/libopensc/card-flex.c
@@ -1127,10 +1127,10 @@ static int flex_generate_key(sc_card_t *card, struct sc_cardctl_cryptoflex_genke
 	apdu.lc = 4;
 
 	/* Little endian representation of exponent */
-	sbuf[0] = data->exponent;
-	sbuf[1] = data->exponent >> 8;
-	sbuf[2] = data->exponent >> 16;
-	sbuf[3] = data->exponent >> 24;
+	sbuf[0] = data->exponent & 0xFF;
+	sbuf[1] = (data->exponent >> 8) & 0xFF;
+	sbuf[2] = (data->exponent >> 16) & 0xFF;
+	sbuf[3] = (data->exponent >> 24) & 0xFF;
 
 	r = sc_transmit_apdu(card, &apdu);
 	SC_TEST_RET(card->ctx, SC_LOG_DEBUG_NORMAL, r, "APDU transmit failed");
diff --git a/src/libopensc/card-mcrd.c b/src/libopensc/card-mcrd.c
index 3b4481ce..23c59fb0 100644
--- a/src/libopensc/card-mcrd.c
+++ b/src/libopensc/card-mcrd.c
@@ -500,8 +500,8 @@ static int get_se_num_from_keyd(sc_card_t * card, unsigned short fid,
 	char dbgbuf[2048];
 	u8 fidbuf[2];
 
-	fidbuf[0] = fid >> 8;
-	fidbuf[1] = fid;
+	fidbuf[0] = (fid >> 8) & 0xFF;
+	fidbuf[1] = fid & 0xFF;
 
 	dfi = get_df_info(card);
 	if (!dfi || !dfi->keyd_file) {
@@ -1271,7 +1271,7 @@ static int mcrd_set_security_env(sc_card_t * card,
 
 	if (card->type == SC_CARD_TYPE_MCRD_DTRUST
 	    || card->type == SC_CARD_TYPE_MCRD_GENERIC) {
-		unsigned short fid;
+		unsigned char fid;
 
 		fid = env->key_ref[0];
 		*p = fid;