diff --git a/page_manager.install b/page_manager.install
index 0e25f7b..6430b3d 100644
--- a/page_manager.install
+++ b/page_manager.install
@@ -32,3 +32,24 @@ function page_manager_requirements($phase) {
 function page_manager_update_8001() {
   \Drupal::service('module_installer')->install(['page_manager_ui']);
 }
+
+/**
+ * Add css_classes and css_id to the existing config schema.
+ */
+function page_manager_update_8002() {
+  $config_factory = \Drupal::configFactory();
+  foreach ($config_factory->listAll('page_manager.page_variant.') as $config_name) {
+    $config = $config_factory->getEditable($config_name);
+    $blocks = $config->get('variant_settings.blocks');
+    foreach ($blocks as $block_id => $block) {
+      if (empty($block['css_classes'])) {
+        $block['css_classes'] = '';
+      }
+      if (empty($block['css_id'])) {
+        $block['css_id'] = '';
+      }
+      $config->set('variant_settings.blocks.' . $block_id, $block);
+    }
+    $config->save(TRUE);
+  }
+}
\ No newline at end of file