diff --git a/templates/thread.html b/templates/thread.html
index 6222b9926..7a2d6ee2e 100644
--- a/templates/thread.html
+++ b/templates/thread.html
@@ -6,6 +6,8 @@
     <meta http-equiv="Content-Security-Policy" content="script-src 'self';">
     <!-- Bootstrap CSS -->
     <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
+    <!-- Custom CSS additions -->
+    <style>img { max-width:100%; height:auto; }</style>
     <title>Converse: {{ title }}</title>
   </head>
   <body>
