diff --git a/epub.php b/epub.php
index dae0171..3f07262 100644
--- a/epub.php
+++ b/epub.php
@@ -21,7 +21,7 @@
 			$nodeHTML = str_replace('</aside', '</i></b', $nodeHTML);
 			$innerHTML .= $nodeHTML;
 		}
-		return '<div>' . strip_tags($innerHTML, '<p><b><h2><i>') . '</div>';
+		return '<div>' . strip_tags($innerHTML, '<p><b><h2><i><strong>') . '</div>';
 	}
 
 	function add_mp_article($url, $context, $epub)