diff --git a/core/lib/Drupal/Core/Theme/Registry.php b/core/lib/Drupal/Core/Theme/Registry.php
index a0af702..b80dbeb 100644
--- a/core/lib/Drupal/Core/Theme/Registry.php
+++ b/core/lib/Drupal/Core/Theme/Registry.php
@@ -351,7 +351,7 @@ protected function build() {
     }
 
     // And then the same thing, but for the theme.
-    if ($this->theme->getEngine()) {
+    if (FALSE && $this->theme->getEngine()) {
       $this->processExtension($cache, $this->theme->getEngine(), 'theme_engine', $this->theme->getName(), $this->theme->getPath());
     }
 
diff --git a/core/modules/layout_discovery/tests/src/Kernel/LayoutTest.php b/core/modules/layout_discovery/tests/src/Kernel/LayoutTest.php
index 9d4c446..c3785df 100644
--- a/core/modules/layout_discovery/tests/src/Kernel/LayoutTest.php
+++ b/core/modules/layout_discovery/tests/src/Kernel/LayoutTest.php
@@ -34,6 +34,17 @@ protected function setUp() {
   }
 
   /**
+   * Tests that a layout provided by a theme has the preprocess function set.
+   */
+  public function testThemeProvidedLayout() {
+    $this->container->get('theme_installer')->install(['test_layout_theme']);
+    $this->config('system.theme')->set('default', 'test_layout_theme')->save();
+
+    $theme_definitions = $this->container->get('theme.registry')->get();
+    $this->assertTrue(in_array('template_preprocess_layout', $theme_definitions['test_layout_theme']['preprocess functions']));
+  }
+
+  /**
    * Test rendering a layout.
    *
    * @dataProvider renderLayoutData
diff --git a/core/modules/layout_discovery/tests/themes/test_layout_theme/templates/test-layout-theme.html.twig b/core/modules/layout_discovery/tests/themes/test_layout_theme/templates/test-layout-theme.html.twig
new file mode 100644
index 0000000..67675f6
--- /dev/null
+++ b/core/modules/layout_discovery/tests/themes/test_layout_theme/templates/test-layout-theme.html.twig
@@ -0,0 +1 @@
+{{ content.content }}
diff --git a/core/modules/layout_discovery/tests/themes/test_layout_theme/test_layout_theme.info.yml b/core/modules/layout_discovery/tests/themes/test_layout_theme/test_layout_theme.info.yml
new file mode 100644
index 0000000..021d43f
--- /dev/null
+++ b/core/modules/layout_discovery/tests/themes/test_layout_theme/test_layout_theme.info.yml
@@ -0,0 +1,6 @@
+name: 'Test layout theme'
+type: theme
+description: 'Theme for testing a theme-provided layout'
+version: VERSION
+base theme: classy
+core: 8.x
diff --git a/core/modules/layout_discovery/tests/themes/test_layout_theme/test_layout_theme.layouts.yml b/core/modules/layout_discovery/tests/themes/test_layout_theme/test_layout_theme.layouts.yml
new file mode 100644
index 0000000..9da19dd
--- /dev/null
+++ b/core/modules/layout_discovery/tests/themes/test_layout_theme/test_layout_theme.layouts.yml
@@ -0,0 +1,7 @@
+test_layout_theme:
+  label: 'Test Layout - Theme'
+  category: 'Test Layout Theme'
+  template: templates/test-layout-theme
+  regions:
+    content:
+      label: Content