diff --git a/core/modules/system/src/Tests/Render/HtmlResponseAttachmentsTest.php b/core/modules/system/src/Tests/Render/HtmlResponseAttachmentsTest.php
index 02497fb..d8bcddb 100644
--- a/core/modules/system/src/Tests/Render/HtmlResponseAttachmentsTest.php
+++ b/core/modules/system/src/Tests/Render/HtmlResponseAttachmentsTest.php
@@ -101,4 +101,26 @@ public function testAttachments() {
     $this->assertHeader('X-Drupal-Cache', 'HIT');
   }
 
+  /**
+   * Test caching of ['#attached'].
+   */
+  public function testSmartCache() {
+    // Make sure our test block is visible.
+    $this->drupalPlaceBlock('drupal_process_attached_block', ['region' => 'content']);
+
+    // Get the front page, which should now have our visible block.
+    $this->drupalGet('');
+    // Make sure our block is visible.
+    $this->assertText('Headers handled by drupal_process_attached().');
+    // The header added in the block build should be present.
+    $this->assertHeader('X-DPA-Cache-Test', 'HIT');
+
+    // Reload the page, to test caching.
+    $this->drupalGet('');
+    // Make sure our block is visible.
+    $this->assertText('Headers handled by drupal_process_attached().');
+    // The header should be present again.
+    $this->assertHeader('X-DPA-Cache-Test', 'HIT');
+  }
+
 }
diff --git a/core/modules/system/tests/modules/render_attached_test/render_attached_test.info.yml b/core/modules/system/tests/modules/render_attached_test/render_attached_test.info.yml
index db4ff45..111fb96 100644
--- a/core/modules/system/tests/modules/render_attached_test/render_attached_test.info.yml
+++ b/core/modules/system/tests/modules/render_attached_test/render_attached_test.info.yml
@@ -4,3 +4,5 @@ description: 'Support module for HtmlResponseAttachmentsTest.'
 package: Testing
 version: VERSION
 core: 8.x
+dependencies:
+  - block
diff --git a/core/modules/system/tests/modules/render_attached_test/src/Plugin/Block/DrupalProcessAttachedBlock.php b/core/modules/system/tests/modules/render_attached_test/src/Plugin/Block/DrupalProcessAttachedBlock.php
new file mode 100644
index 0000000..9ab5400
--- /dev/null
+++ b/core/modules/system/tests/modules/render_attached_test/src/Plugin/Block/DrupalProcessAttachedBlock.php
@@ -0,0 +1,42 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\render_attached_test\Plugin\Block\DrupalProcessAttachedBlock.
+ */
+
+namespace Drupal\render_attached_test\Plugin\Block;
+
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Cache\Cache;
+
+/**
+ * A block we can use to test caching of #attached headers.
+ *
+ * @Block(
+ *   id = "drupal_process_attached_block",
+ *   admin_label = @Translation("DrupalProcessAttachedBlock")
+ * )
+ *
+ * @see \Drupal\system\Tests\Render\HtmlResponseAttachmentsTest
+ */
+class DrupalProcessAttachedBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    // Use drupal_process_attached() to attach an HTTP header.
+    \drupal_process_attached(['#attached' => ['http_header' => [['X-DPA-Cache-Test', 'HIT']]]]);
+    // Return some arbitrary markup so the block doesn't disappear.
+    return ['#markup' => 'Headers handled by drupal_process_attached().'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheMaxAge() {
+    return Cache::PERMANENT;
+  }
+
+}