diff -u b/config_entity_example/lib/Drupal/config_entity_example/Form/RobotFormBase.php b/config_entity_example/lib/Drupal/config_entity_example/Form/RobotFormBase.php
--- b/config_entity_example/lib/Drupal/config_entity_example/Form/RobotFormBase.php
+++ b/config_entity_example/lib/Drupal/config_entity_example/Form/RobotFormBase.php
@@ -8,7 +8,9 @@
 namespace Drupal\config_entity_example\Form;
 
 use Drupal\Core\Url;
-use Drupal\Core\Entity\EntityFormController;
+use Drupal\Core\Entity\EntityForm;
+use \Drupal\Core\Entity\Query\QueryFactory;
+use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
  * Class RobotFormBase.
@@ -22,7 +24,46 @@
  *
  * @ingroup config_entity_example
  */
-class RobotFormBase extends EntityFormController {
+class RobotFormBase extends EntityForm {
+
+  /**
+   * @var \Drupal\Core\Entity\Query\QueryFactory
+   */
+  protected $entityQueryFactory;
+
+  /**
+   * Construct the RobotFormBase.
+   *
+   * For simple entity forms, there's no need for a constructor. Our robot form
+   * base, however, requires an entity query factory to be injected into it
+   * from the container. We later use this query factory to build an entity
+   * query for the exists() method.
+   *
+   * @param \Drupal\Core\Entity\Query\QueryFactory $query_factory
+   *  An entity query factory for the robot entity type.
+   */
+  public function __construct(QueryFactory $query_factory) {
+    $this->entityQueryFactory = $query_factory;
+  }
+
+  /**
+   * Factory method for RobotFormBase.
+   *
+   * When Drupal builds this class it does not call the constructor directly.
+   * Instead, it relies on this method to build the new object. Why? The class
+   * constructor may take multiple arguments that are unknown to Drupal. The
+   * create() method always takes one parameter -- the container. The purpose
+   * of the create() method is twofold: It provides a standard way for Drupal
+   * to construct the object, meanwhile it provides you a place to get needed
+   * constructor parameters from the container.
+   *
+   * In this case, we ask the container for an entity query factory. We then
+   * pass the factory to our class as a constructor parameter.
+   *
+   */
+  public static function create(ContainerInterface $container) {
+    return new static($container->get('entity.query'));
+  }
 
   /**
    * Overrides Drupal\Core\Entity\EntityFormController::form().
@@ -61,7 +102,9 @@
       '#title' => $this->t('Machine name'),
       '#default_value' => $robot->id(),
       '#machine_name' => array(
-        'exists' => 'contact_category_load',
+        'exists' => array($this, 'exists'),
+        'replace_pattern' =>'([^a-z0-9_]+)|(^custom$)',
+        'error' => 'The machine-readable name must be unique, and can only contain lowercase letters, numbers, and underscores. Additionally, it can not be the reserved word "custom".',
       ),
       '#disabled' => !$robot->isNew(),
     );
@@ -71,6 +114,31 @@
   }
 
   /**
+   * Checks for an existing robot.
+   *
+   * @param string|int $entity_id
+   *   The entity ID.
+   * @param array $element
+   *   The form element.
+   * @param array $form_state
+   *   The form state.
+   *
+   * @return bool
+   *   TRUE if this format already exists, FALSE otherwise.
+   */
+  public function exists($entity_id, array $element, array $form_state) {
+    // Use the query factory to build a new robot entity query.
+    $query = $this->entityQueryFactory->get('robot');
+
+    // Query the entity ID to see if its in use.
+    $result = $query->condition('id', $element['#field_prefix'] . $entity_id)
+      ->execute();
+
+    // We don't need to return the ID, only if it exists or not.
+    return (bool) $result;
+  }
+
+  /**
    * Overrides Drupal\Core\Entity\EntityFormController::actions().
    *
    * To set the submit button text, we need to override actions().
diff -u b/config_entity_example/lib/Drupal/config_entity_example/Tests/ConfigEntityExampleTest.php b/config_entity_example/lib/Drupal/config_entity_example/Tests/ConfigEntityExampleTest.php
--- b/config_entity_example/lib/Drupal/config_entity_example/Tests/ConfigEntityExampleTest.php
+++ b/config_entity_example/lib/Drupal/config_entity_example/Tests/ConfigEntityExampleTest.php
@@ -31,7 +31,7 @@
    * Various functional test of the Config Entity Example module.
    *
    * 1) Verify that the Marvin entity was created when the module was installed.
-   * 
+   *
    * 2) Verify that permissions are applied to the various defined paths.
    *
    * 3) Verify that we can manage entities through the user interface.
@@ -77,7 +77,7 @@
       $this->drupalGet($unforbidden);
       $this->assertResponse(200, "Access granted to admin user for path: $unforbidden");
     }
-    
+
     // 3) Verify that we can manage entities through the user interface.
     // We still have the admin user logged in, so we'll create, update, and
     // delete an entity.