diff --git a/src/highlight.js b/src/highlight.js
index 7974033794..946dafa817 100644
--- a/src/highlight.js
+++ b/src/highlight.js
@@ -819,8 +819,18 @@ const HLJS = function(hljs) {
    * auto-highlights all pre>code elements on the page
    */
   function highlightAll() {
+    function boot() {
+      // if a highlight was requested before DOM was loaded, do now
+      highlightAll();
+      window.removeEventListener('DOMContentLoaded', boot, false);
+    }
+
     // if we are called too early in the loading process
     if (document.readyState === "loading") {
+      // make sure the event listener is only added once
+      if (!wantsHighlight) {
+        window.addEventListener('DOMContentLoaded', boot, false);
+      }
       wantsHighlight = true;
       return;
     }
@@ -829,16 +839,6 @@ const HLJS = function(hljs) {
     blocks.forEach(highlightElement);
   }
 
-  function boot() {
-    // if a highlight was requested before DOM was loaded, do now
-    if (wantsHighlight) highlightAll();
-  }
-
-  // make sure we are in the browser environment
-  if (typeof window !== 'undefined' && window.addEventListener) {
-    window.addEventListener('DOMContentLoaded', boot, false);
-  }
-
   /**
    * Register a language grammar module
    *