diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index d26250c..069a743 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -1649,7 +1649,7 @@ protected function drupalPostForm($path, $edit, $submit, array $options = array(
         $action = isset($form['action']) ? $this->getAbsoluteUrl((string) $form['action']) : $this->getUrl();
         if ($ajax) {
           if (empty($submit['path'])) {
-            throw new \Exception('Missing ajax path specified');
+            throw new \Exception('No #ajax path specified.');
           }
           $action = $this->getAbsoluteUrl($submit['path']);
           // Ajax callbacks verify the triggering element if necessary, so while
@@ -1828,7 +1828,7 @@ protected function drupalPostAjaxForm($path, $edit, $triggering_element, $ajax_p
     }
 
     if (empty($ajax_path)) {
-      throw new \Exception('Missing ajax path specified');
+      throw new \Exception('No #ajax path specified.');
     }
 
     $ajax_path = $this->container->get('unrouted_url_assembler')->assemble('base://' . $ajax_path, $options);