diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index ecc150a..ced9c4c 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -518,7 +518,8 @@ function watchdog_exception($type, Exception $exception, $message = NULL, $varia
  *   (optional) The translated message to be displayed to the user. For
  *   consistency with other messages, it should begin with a capital letter and
  *   end with a period. A render array may also be provided for markup, but
- *   #attached is not supported.
+ *   #attached is not supported. Additionally, any cache tags and contexts are
+ *   ignored, however this is okay because page caching is disabled.
  * @param string $type
  *   (optional) The message's type. Defaults to 'status'. These values are
  *   supported:
@@ -573,9 +574,9 @@ function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE)
     // (like assets) should not be supported.
     if (is_array($message)) {
       $rendered_message = \Drupal::service('renderer')->renderPlain($message);
-      // The rendering will have bubbled any #attached assets to the top level
-      // of $message. Assert that there are none.
-      assert('empty($message[\'#attached\']);', 'Render arrays passed to drupal_set_message() cannot have attached assets.');
+      // The rendering will have all attachments bubbled to #attached in the top
+      // level of $message. Assert that there are none.
+      assert('empty($message[\'#attached\']);', 'Render arrays passed to drupal_set_message() cannot have attachments.');
       $message = $rendered_message;
     }
 
diff --git a/core/modules/system/src/Tests/Bootstrap/DrupalSetMessageTest.php b/core/modules/system/src/Tests/Bootstrap/DrupalSetMessageTest.php
index e345f37..1d57018 100644
--- a/core/modules/system/src/Tests/Bootstrap/DrupalSetMessageTest.php
+++ b/core/modules/system/src/Tests/Bootstrap/DrupalSetMessageTest.php
@@ -61,7 +61,7 @@ function testDrupalSetMessage() {
 
     // Ensure render arrays fail with #attached when assertions are enabled.
     $this->drupalGet('system-test/drupal-set-message-fail');
-    $this->assertText('Render arrays passed to drupal_set_message() cannot have attached assets.');
+    $this->assertText('Render arrays passed to drupal_set_message() cannot have attachments.');
   }
 
   /**
@@ -69,10 +69,11 @@ function testDrupalSetMessage() {
    */
   protected function error($message = '', $group = 'Other', array $caller = NULL) {
     // @todo Clean this up in https://www.drupal.org/node/2536560.
-    if (strpos($message, 'Render arrays passed to drupal_set_message() cannot have attached assets.') !== FALSE) {
+    if (strpos($message, 'Render arrays passed to drupal_set_message() cannot have attachments.') !== FALSE) {
       // We're expecting this error.
       return FALSE;
     }
-    parent::error($message, $group, $caller);
+    return parent::error($message, $group, $caller);
   }
+
 }