diff -u b/core/modules/system/src/Form/ModulesListForm.php b/core/modules/system/src/Form/ModulesListForm.php
--- b/core/modules/system/src/Form/ModulesListForm.php
+++ b/core/modules/system/src/Form/ModulesListForm.php
@@ -430,7 +430,7 @@
     }
 
     // Set id for checkbox here so module label can reference it.
-    $id = Unicode::strtolower(Html::cleanCssIdentifier('edit-modules-' . $module->info['package'] . '-' . $module->getName() . '-enable'));
+    $id = Html::getClass('edit-modules-' . $module->info['package'] . '-' . $module->getName() . '-enable');
 
     $row['enable'] += array(
       '#id' => $id,