bgpq3 does not compile on ubuntu about bgpq3 HOT 2 CLOSED

diff --git a/sx_prefix.c b/sx_prefix.c
index 07d4e9b..df8bf43 100644
--- a/sx_prefix.c
+++ b/sx_prefix.c
@@ -195,10 +195,10 @@ sx_prefix_range_parse(struct sx_radix_tree* tree, int af, int maxlen,
    } else if (d[1] == '+') {
        min=p.masklen;
        max=maxlen;
-   } else if (isnumber(d[1])) {
+   } else if (isdigit(d[1])) {
        char* dm = NULL;
        min = strtoul(d+1, &dm, 10);
-       if (dm && *dm == '-' && isnumber(dm[1])) {
+       if (dm && *dm == '-' && isdigit(dm[1])) {
            max = strtoul(dm+1, NULL, 10);
        } else if (dm && *dm) {
            sx_report(SX_ERROR, "Unable to parse prefix-range %s\n", text);