diff --git a/src/newusers.c b/src/newusers.c
index a8df7c1b75..d71f7f5c65 100644
--- a/src/newusers.c
+++ b/src/newusers.c
@@ -236,7 +236,7 @@ static int add_group (const char *name, const char *gid, gid_t *ngid, uid_t uid)
 		return 0;
 	}
 
-	if (isdigit_c(gid[0])) {
+	if (!streq(gid, "") && strisdigit_c(gid)) {
 		/*
 		 * The GID is a number, which means either this is a brand
 		 * new group, or an existing group.
@@ -280,7 +280,7 @@ static int add_group (const char *name, const char *gid, gid_t *ngid, uid_t uid)
 	/*
 	 * Now I have all of the fields required to create the new group.
 	 */
-	if (!streq(gid, "") && (!isdigit_c(gid[0]))) {
+	if (!streq(gid, "") && !strisdigit_c(gid)) {
 		grent.gr_name = xstrdup (gid);
 	} else {
 		grent.gr_name = xstrdup (name);
@@ -345,7 +345,7 @@ static int get_user_id (const char *uid, uid_t *nuid) {
 	 * The first guess for the UID is either the numerical UID that the
 	 * caller provided, or the next available UID.
 	 */
-	if (isdigit_c(uid[0])) {
+	if (!streq(uid, "") && strisdigit_c(uid)) {
 		if ((get_uid(uid, nuid) == -1) || (*nuid == (uid_t)-1)) {
 			fprintf (stderr,
 			         _("%s: invalid user ID '%s'\n"),