diff --git a/components/select.inc b/components/select.inc
index 495051b..ec1df77 100644
--- a/components/select.inc
+++ b/components/select.inc
@@ -118,6 +118,7 @@ function _webform_edit_select($component) {
       '#key_type' => 'mixed',
       '#key_type_toggle' => t('Customize keys (Advanced)'),
       '#key_type_toggled' => $component['extra']['custom_keys'],
+      '#default_value_pattern' => '^%.+\[.+\]$',
       '#disabled' => !empty($component['extra']['options_source']),
       '#weight' => 1,
     );