diff --git a/src/libopensc/card-cac.c b/src/libopensc/card-cac.c
index 9f7b660c..0098830c 100644
--- a/src/libopensc/card-cac.c
+++ b/src/libopensc/card-cac.c
@@ -951,12 +951,13 @@ static int cac_get_challenge(sc_card_t *card, u8 *rnd, size_t len)
 {
 	/* CAC requires 8 byte response */
 	u8 rbuf[8];
+	u8 *rbufp = &rbuf[0];
 	size_t out_len = sizeof rbuf;
 	int r;
 
 	LOG_FUNC_CALLED(card->ctx);
 
-	r = cac_apdu_io(card, 0x84, 0x00, 0x00, NULL, 0, (u8 **) &rbuf, &out_len);
+	r = cac_apdu_io(card, 0x84, 0x00, 0x00, NULL, 0, &rbufp, &out_len);
 	LOG_TEST_RET(card->ctx, r, "Could not get challenge");
 
 	if (len < out_len) {