diff --git a/ui/ui.core.inc b/ui/ui.core.inc
index 70d75a9..6af9541 100644
--- a/ui/ui.core.inc
+++ b/ui/ui.core.inc
@@ -430,7 +430,9 @@ class RulesPluginUI extends FacesExtender implements RulesPluginUIInterface {
     $form['settings']['name'] = array(
       '#type' => 'machine_name',
       '#default_value' => isset($machine_name) ? $machine_name : '',
-      '#maxlength' => 64,
+      // The string 'rules_' is pre-pended to machine names, so the
+      // maxlength must be less than the field length of 64 characters.
+      '#maxlength' => 58,
       '#disabled' => entity_has_status('rules_config', $this->element, ENTITY_IN_CODE) && !(isset($form_state['op']) && $form_state['op'] == 'clone'),
       '#machine_name' => array(
         'exists' => 'rules_config_load',