s = ds_cstr(&line);
if (*reply_code == -1) {
- if (!isdigit(s[0]) || !isdigit(s[1]) || !isdigit(s[2])) {
+ if (!isdigit((unsigned char)s[0])
+ || !isdigit((unsigned char)s[1])
+ || !isdigit((unsigned char)s[2])) {
VLOG_WARN("reply from %s does not start with 3-digit code",
client->connect_path);
error = EPROTO;