Index: t3lib/class.t3lib_div.php
===================================================================
--- t3lib/class.t3lib_div.php	(Revision 6908)
+++ t3lib/class.t3lib_div.php	(Arbeitskopie)
@@ -1552,7 +1552,10 @@
 	 * @return	boolean		Whether the given URL is valid
 	 */
 	public static function isValidUrl($url) {
-		return (filter_var($url, FILTER_VALIDATE_URL, FILTER_FLAG_SCHEME_REQUIRED) !== false);
+		// Same effect of using filter_var with FILTER_VALIDATE_URL and
+		// FILTER_FLAG_SCHEME_REQUIRED but is PHP 5.1 compatible:
+		$parsed = @parse_url($url);
+		return (is_array($parsed) && isset($parsed['scheme']));
 	}