diff --git a/default.epub3 b/default.epub3
index ccd34ba85..57f090b6a 100644
--- a/default.epub3
+++ b/default.epub3
@@ -16,7 +16,7 @@ $highlighting-css$
   </style>
 $endif$
 $for(css)$
-  <link rel="stylesheet" href="$css$" />
+  <link rel="stylesheet" type="text/css" href="$css$" />
 $endfor$
 </head>
 <body>
