diff --git a/core/imageboard.pack.php b/core/imageboard.pack.php
index 517b5a5c..d56d561c 100644
--- a/core/imageboard.pack.php
+++ b/core/imageboard.pack.php
@@ -1055,9 +1055,10 @@ class Tag {
 	 */
 	public static function sanitise($tag) {
 		assert(is_string($tag));
-		$tag = preg_replace("/[\s?*]/", "", $tag);
-		$tag = preg_replace("/\.+/", ".", $tag);
-		$tag = preg_replace("/^(\.+[\/\\\\])+/", "", $tag);
+		$tag = preg_replace("/[\s?*]/", "", $tag);            # whitespace
+		$tag = preg_replace('/\x20(\x0e|\x0f)/', '', $tag);   # unicode RTL
+		$tag = preg_replace("/\.+/", ".", $tag);              # strings of dots?
+		$tag = preg_replace("/^(\.+[\/\\\\])+/", "", $tag);   # trailing slashes?
 		return $tag;
 	}