diff --git a/boards/static/js/main.js b/boards/static/js/main.js
--- a/boards/static/js/main.js
+++ b/boards/static/js/main.js
@@ -23,14 +23,16 @@
  for the JavaScript code in this page.
  */
 
-var LOCALE = window.navigator.language;
-var FORMATTER = new Intl.DateTimeFormat(
-    LOCALE,
-    {
-        weekday: 'short', year: 'numeric', month: 'short', day: 'numeric',
-        hour: 'numeric', minute: '2-digit', second: '2-digit'
-    }
-);
+if (window.Intl) {
+    var LOCALE = window.navigator.language;
+    var FORMATTER = new Intl.DateTimeFormat(
+            LOCALE,
+            {
+                weekday: 'short', year: 'numeric', month: 'short', day: 'numeric',
+                hour: 'numeric', minute: '2-digit', second: '2-digit'
+            }
+    );
+}
 
 /**
  * An email is a hidden file to prevent spam bots from posting. It has to be
@@ -53,6 +55,10 @@ function highlightCode(node) {
  * Translate timestamps to local ones for all <time> tags inside node.
  */
 function translate_time(node) {
+    if (window.Intl === null) {
+        return;
+    }
+
     var elements;
 
     if (node === null) {
diff --git a/boards/templates/boards/post.html b/boards/templates/boards/post.html
--- a/boards/templates/boards/post.html
+++ b/boards/templates/boards/post.html
@@ -26,7 +26,7 @@
     {% endcomment %}
     {% if thread.archived %}
         {% if is_opening %}
-        — {{ thread.bump_time }}
+        — <time datetime="{{ thread.bump_time|date:'c' }}">{{ thread.bump_time|date:'r' }}</time>
         {% endif %}
     {% endif %}
     {% if is_opening and need_open_link %}