diff --git a/synapse/static/index.html b/synapse/static/index.html
index d3f1c7dce0..bf46df9097 100644
--- a/synapse/static/index.html
+++ b/synapse/static/index.html
@@ -48,13 +48,13 @@
     </div>
     <h1>It works! Synapse is running</h1>
     <p>Your Synapse server is listening on this port and is ready for messages.</p>
-    <p>To use this server you'll need <a href="https://matrix.org/docs/projects/try-matrix-now.html#clients" target="_blank">a Matrix client</a>.
+    <p>To use this server you'll need <a href="https://matrix.org/docs/projects/try-matrix-now.html#clients" target="_blank" rel="noopener noreferrer">a Matrix client</a>.
     </p>
     <p>Welcome to the Matrix universe :)</p>
     <hr>
     <p>
       <small>
-        <a href="https://matrix.org" target="_blank">
+        <a href="https://matrix.org" target="_blank" rel="noopener noreferrer">
           matrix.org
         </a>
       </small>