diff --git a/system/libraries/Form_validation.php b/system/libraries/Form_validation.php
index 1ed5084..40ba012 100644
--- a/system/libraries/Form_validation.php
+++ b/system/libraries/Form_validation.php
@@ -1405,7 +1405,7 @@
 	 */
 	public function valid_base64($str)
 	{
-		return ! preg_match('/[^a-zA-Z0-9\/\+=]/', $str);
+		return (base64_encode(base64_decode($str)) === $str);
 	}
 
 	// --------------------------------------------------------------------