diff --git a/lib/nss.c b/lib/nss.c
index cea836b23..6c8c90105 100644
--- a/lib/nss.c
+++ b/lib/nss.c
@@ -696,8 +696,10 @@ static void display_conn_info(struct connectdata *conn, PRFileDesc *sock)
       }
       Curl_ssl_init_certinfo(conn->data, i);
       for(i = 0; cert; cert = cert2) {
-        Curl_extract_certinfo(conn, i++, cert->derCert.data,
-                              cert->derCert.data + cert->derCert.len);
+        Curl_extract_certinfo(conn, i++,
+                              (unsigned char *) cert->derCert.data,
+                              (unsigned char *) cert->derCert.data +
+                                                cert->derCert.len);
         if(cert->isRoot) {
           CERT_DestroyCertificate(cert);
           break;