diff --git a/lib/isc/crc64.c b/lib/isc/crc64.c
index e83cdc02a4..8869a5cc0e 100644
--- a/lib/isc/crc64.c
+++ b/lib/isc/crc64.c
@@ -123,12 +123,14 @@ isc_crc64_init(isc_uint64_t *crc) {
 
 void
 isc_crc64_update(isc_uint64_t *crc, const isc_uint8_t *data, size_t len) {
-	unsigned char *p = data;
+	unsigned char *p;
 	int i;
 
 	REQUIRE(crc != NULL);
 	REQUIRE(data != NULL);
 
+	DE_CONST(data, p);
+
 	while (len-- > 0) {
 		i = ((int) (*crc >> 56) ^ *p++) & 0xff;
 		*crc = crc64_table[i] ^ (*crc << 8);