diff --git a/include/class.format.php b/include/class.format.php
index 7c5bc2ad47996fe5f6da65ad4956d49f506418c7..c6effb45b959d73d2d8b59523e727db2f1742c08 100644
--- a/include/class.format.php
+++ b/include/class.format.php
@@ -321,7 +321,7 @@ class Format {
             'hook_tag' => function($e, $a=0) { return Format::__html_cleanup($e, $a); },
             'elements' => '*+iframe',
             'spec' =>
-            'iframe=-*,height,width,type,style,src(match="`^(https?:)?//(www\.)?(youtube|dailymotion|vimeo|player.vimeo)\.com/`i"),frameborder'.($options['spec'] ? '; '.$options['spec'] : ''),
+            'iframe=-*,height,width,type,style,src(match="`^(https?:)?//(www\.)?(youtube|dailymotion|vimeo|player.vimeo)\.com/`i"),frameborder'.($options['spec'] ? '; '.$options['spec'] : '').',allowfullscreen',
         );
 
         return Format::html($html, $config);