diff --git a/group.php b/group.php
index 6e773ae82..acae6e4ee 100644
--- a/group.php
+++ b/group.php
@@ -199,14 +199,30 @@ if (!$group_id) {
 
     if (!empty($_POST['add']) || !empty($_POST['remove']) || !empty($_POST['approve']) || !empty($_POST['deny'])) {
         if (!$is_moderator) {
+            set_die_append_msg(false, false, $group_id);
             bb_die($lang['NOT_GROUP_MODERATOR']);
         }
 
         if (!empty($_POST['add'])) {
             if (isset($_POST['username']) && !($row = get_userdata($_POST['username'], true))) {
+                set_die_append_msg(false, false, $group_id);
                 bb_die($lang['COULD_NOT_ADD_USER']);
             }
 
+            // Prevent adding moderator
+            if ($row['user_id'] == $group_moderator) {
+                set_die_append_msg(false, false, $group_id);
+                bb_die(sprintf($lang['USER_IS_MOD_GROUP'], profile_url($row)));
+            }
+
+            // Prevent infinity user adding into group
+            if ($is_member = DB()->fetch_row("SELECT user_id FROM " . BB_USER_GROUP . " WHERE group_id = $group_id AND user_id = " . $row['user_id'] . " LIMIT 1")) {
+                if ($is_member['user_id']) {
+                    set_die_append_msg(false, false, $group_id);
+                    bb_die(sprintf($lang['USER_IS_MEMBER_GROUP'], profile_url($row)));
+                }
+            }
+
             \TorrentPier\Legacy\Group::add_user_into_group($group_id, $row['user_id']);
 
             if ($bb_cfg['group_send_email']) {
@@ -234,6 +250,7 @@ if (!$group_id) {
                     $sql_in[] = (int)$members_id;
                 }
                 if (!$sql_in = implode(',', $sql_in)) {
+                    set_die_append_msg(false, false, $group_id);
                     bb_die($lang['NONE_SELECTED']);
                 }
 
diff --git a/library/language/source/main.php b/library/language/source/main.php
index e88356fd0..48a2b371e 100644
--- a/library/language/source/main.php
+++ b/library/language/source/main.php
@@ -725,7 +725,8 @@ $lang['GROUP_REQUEST'] = 'A request to join your group has been made.';
 $lang['GROUP_APPROVED'] = 'Your request has been approved.';
 $lang['GROUP_ADDED'] = 'You have been added to this usergroup.';
 $lang['ALREADY_MEMBER_GROUP'] = 'You are already a member of this group';
-$lang['USER_IS_MEMBER_GROUP'] = 'User is already a member of this group';
+$lang['USER_IS_MEMBER_GROUP'] = '%s is already a member of this group';
+$lang['USER_IS_MOD_GROUP'] = '%s is a moderator of this group';
 $lang['GROUP_TYPE_UPDATED'] = 'Successfully updated group type.';
 $lang['EFFECTIVE_DATE'] = 'Effective Date';