diff --git a/mod/assign/classes/output/renderer.php b/mod/assign/classes/output/renderer.php
index 098fd15c419..646414969a2 100644
--- a/mod/assign/classes/output/renderer.php
+++ b/mod/assign/classes/output/renderer.php
@@ -246,7 +246,7 @@ class renderer extends \plugin_renderer_base {
 
         $description = $header->preface;
         if ($header->showintro || $header->activity) {
-            $description = $this->output->box_start('generalbox boxaligncenter', 'intro');
+            $description = $this->output->box_start('generalbox boxaligncenter');
             if ($header->showintro) {
                 $description .= format_module_intro('assign', $header->assign, $header->coursemoduleid);
             }