diff --git a/inc/anti-bot.php b/inc/anti-bot.php
index 9260b237..9e3ffeb2 100644
--- a/inc/anti-bot.php
+++ b/inc/anti-bot.php
@@ -180,9 +180,9 @@ function _create_antibot($board, $thread) {
 	query('DELETE FROM `antispam` WHERE `expires` < UNIX_TIMESTAMP()') or error(db_error());
 	
 	if ($thread)
-		$query = prepare('UPDATE `antispam` SET `expires` = UNIX_TIMESTAMP() + :expires WHERE `board` = :board AND `thread` = :thread');
+		$query = prepare('UPDATE `antispam` SET `expires` = UNIX_TIMESTAMP() + :expires WHERE `board` = :board AND `thread` = :thread AND `expires` IS NULL');
 	else
-		$query = prepare('UPDATE `antispam` SET `expires` = UNIX_TIMESTAMP() + :expires WHERE `board` = :board AND `thread` IS NULL');
+		$query = prepare('UPDATE `antispam` SET `expires` = UNIX_TIMESTAMP() + :expires WHERE `board` = :board AND `thread` IS NULL AND `expires` IS NULL');
 	
 	$query->bindValue(':board', $board);
 	if ($thread)