diff --git a/src/Whoops/Resources/views/header.html.php b/src/Whoops/Resources/views/header.html.php
index 2ee31e5..11e1c1d 100644
--- a/src/Whoops/Resources/views/header.html.php
+++ b/src/Whoops/Resources/views/header.html.php
@@ -22,7 +22,7 @@
     <ul class="search-for-help">
       <?php if (!empty($docref_url)): ?>
       <li>
-        <a rel="noopener" rel="noreferrer" target="_blank" href="<?php echo $docref_url; ?>" title="Search for help in the PHP manual.">
+        <a rel="noopener noreferrer" target="_blank" href="<?php echo $docref_url; ?>" title="Search for help in the PHP manual.">
           <!-- PHP icon by Icons Solid -->
           <!-- https://www.iconfinder.com/icons/322421/book_icon -->
           <!-- Free for commercial use -->
@@ -31,7 +31,7 @@
       </li>
       <?php endif ?>
       <li>
-        <a rel="noopener" rel="noreferrer" target="_blank" href="https://google.com/search?q=<?php echo urlencode(implode('\\', $name).' '.$message) ?>" title="Search for help on Google.">
+        <a rel="noopener noreferrer" target="_blank" href="https://google.com/search?q=<?php echo urlencode(implode('\\', $name).' '.$message) ?>" title="Search for help on Google.">
           <!-- Google icon by Alfredo H, from https://www.iconfinder.com/alfredoh -->
           <!-- Creative Commons (Attribution 3.0 Unported) -->
           <!-- http://creativecommons.org/licenses/by/3.0/ -->
@@ -41,7 +41,7 @@
         </a>
       </li>
       <li>
-        <a rel="noopener" rel="noreferrer" target="_blank" href="https://duckduckgo.com/?q=<?php echo urlencode(implode('\\', $name).' '.$message) ?>" title="Search for help on DuckDuckGo.">
+        <a rel="noopener noreferrer" target="_blank" href="https://duckduckgo.com/?q=<?php echo urlencode(implode('\\', $name).' '.$message) ?>" title="Search for help on DuckDuckGo.">
           <!-- DuckDuckGo icon by IconBaandar Team, from https://www.iconfinder.com/iconbaandar -->
           <!-- Creative Commons (Attribution 3.0 Unported) -->
           <!-- http://creativecommons.org/licenses/by/3.0/ -->
@@ -55,7 +55,7 @@
         </a>
       </li>
       <li>
-        <a rel="noopener" rel="noreferrer" target="_blank" href="https://stackoverflow.com/search?q=<?php echo urlencode(implode('\\', $name).' '.$message) ?>" title="Search for help on Stack Overflow.">
+        <a rel="noopener noreferrer" target="_blank" href="https://stackoverflow.com/search?q=<?php echo urlencode(implode('\\', $name).' '.$message) ?>" title="Search for help on Stack Overflow.">
           <!-- Stack Overflow icon by Picons.me, from https://www.iconfinder.com/Picons -->
           <!-- Free for commercial use -->
           <svg class="stackoverflow" height="16" viewBox="-1163 1657.697 56.693 56.693" width="16" xmlns="http://www.w3.org/2000/svg">