diff --git a/outputhtml.php b/outputhtml.php
index 8aa6150..3f9bfac 100644
--- a/outputhtml.php
+++ b/outputhtml.php
@@ -112,7 +112,23 @@ EOT;
     // Manage the timestamp/md5sum for the external files managed by this
     // server.
     $dom = new \DOMDocument ();
-    @$dom->loadHTML ($layoutPage);
+    libxml_use_internal_errors (true);
+    $dom->loadHTML ($layoutPage);
+    $errors = libxml_get_errors ();
+    foreach ($errors as $key => $err)
+    {
+      // Tag YYY invalid : code 801
+      // Like in <nav> <section>
+      if ($err->code === 801)
+        unset ($errors[$key]);
+    }
+    libxml_clear_errors();
+    if (! empty ($errors))
+    {
+      echo "ERROR: Invalid HTML provided\n";
+      echo "<pre>";var_dump ($errors);echo "</pre>";
+      exit;
+    }
     foreach (array ("script" => "src", "link" => "href", "img" => "src")
              as $key=>$val)
     {