diff --git a/index.php b/index.php
index da69b25..207b42b 100644
--- a/index.php
+++ b/index.php
@@ -26,7 +26,7 @@
 	 */
 
 	$start_time = microtime(true);
-	$captcha_str = substr(strtr(sha1($start_time), "1234567890", "ABCDEFGHgh"), 0, 6);
+	$captcha_str = substr(strtr(sha1($start_time), "1234567890ABCDEF", "abdeghjkmnpqtuwx"), 0, 6);
 
 	// Return source code
 	if(isset($_GET['source'])) {