diff --git a/modules/content_multigroup/content_multigroup.node_form.inc b/modules/content_multigroup/content_multigroup.node_form.inc
index f1aa5de..0218eea 100644
--- a/modules/content_multigroup/content_multigroup.node_form.inc
+++ b/modules/content_multigroup/content_multigroup.node_form.inc
@@ -813,6 +813,16 @@ function content_multigroup_add_more_js($type_name_url, $group_name) {
       $form_element[$group_name][$key]['_weight']['#delta'] = $delta;
     }
   }
+  // Let other modules alter it.
+  // We pass an empty array as hook_form_alter's usual 'form_state' parameter,
+  // instead of $form_atate (for reasons we may never remember).
+  // However, this argument is still expected to be passed by-reference
+  // (and PHP5.3 will throw an error if it isn't.) This leads to:
+  $data = &$form_element;
+  $empty_form_state = array();
+  $data['__drupal_alter_by_ref'] = array(&$empty_form_state);
+  drupal_alter('form', $data, 'content_multigroup_add_more_js');
+
   // Add the new element at the right place in the (original, unbuilt) form.
   $success = content_set_nested_elements($form, $group_name, $form_element[$group_name]);