diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index aaa48ff..b9438fb 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1483,31 +1483,6 @@ function theme_settings_convert_to_config(array $theme_settings, Config $config)
 }
 
 /**
- * Renders a system default template, which is essentially a PHP template.
- *
- * @param $template_file
- *   The filename of the template to render.
- * @param $variables
- *   A keyed array of variables that will appear in the output.
- *
- * @return
- *   The output generated by the template.
- */
-function theme_render_template($template_file, $variables) {
-  // Extract the variables to a local namespace
-  extract($variables, EXTR_SKIP);
-
-  // Start output buffering
-  ob_start();
-
-  // Include the template file
-  include DRUPAL_ROOT . '/' . $template_file;
-
-  // End buffering and return its contents
-  return ob_get_clean();
-}
-
-/**
  * Enables a given list of themes.
  *
  * @param $theme_list
diff --git a/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestPhpTemplate.php b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestPhpTemplate.php
new file mode 100644
index 0000000..ff3fd03
--- /dev/null
+++ b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestPhpTemplate.php
@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\system\Tests\Theme\ThemeTestPhpTemplate.
+ */
+
+namespace Drupal\system\Tests\Theme;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Tests theme functions and templates with the PHPTemplate engine.
+ */
+class ThemeTestPhpTemplate extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('theme_test');
+
+  public static function getInfo() {
+    return array(
+      'name' => 'PHPTemplate Engine',
+      'description' => 'Test theme functions with PHPTemplate.',
+      'group' => 'Theme',
+    );
+  }
+
+  function setUp() {
+    parent::setUp();
+    theme_enable(array('test_theme_phptemplate'));
+  }
+
+  /**
+   * Ensures a theme's template is overrideable based on the 'template' filename.
+   */
+  function testTemplateOverride() {
+    config('system.theme')
+      ->set('default', 'test_theme_phptemplate')
+      ->save();
+    $this->drupalGet('theme-test/template-test');
+    $this->assertText('Success: Template overridden.', t('Template overridden by defined \'template\' filename.'));
+  }
+
+}
diff --git a/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php
index 135a435..7860511 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Theme/ThemeTestTwig.php
@@ -24,7 +24,7 @@ class ThemeTestTwig extends WebTestBase {
   public static function getInfo() {
     return array(
       'name' => 'Twig Engine',
-      'description' => 'Test theme functions with twig.',
+      'description' => 'Test Twig-specific theme functionality.',
       'group' => 'Theme',
     );
   }
@@ -35,17 +35,6 @@ function setUp() {
   }
 
   /**
-   * Ensures a themes template is overrideable based on the 'template' filename.
-   */
-  function testTemplateOverride() {
-    config('system.theme')
-      ->set('default', 'test_theme')
-      ->save();
-    $this->drupalGet('theme-test/template-test');
-    $this->assertText('Success: Template overridden.', t('Template overridden by defined \'template\' filename.'));
-  }
-
-  /**
    * Tests that the Twig engine handles PHP data correctly.
    */
   function testTwigVariableDataTypes() {
diff --git a/core/modules/system/tests/themes/test_theme_phptemplate/theme_test.template_test.tpl.php b/core/modules/system/tests/themes/test_theme_phptemplate/theme_test.template_test.tpl.php
index d4409bf..ada11e7 100644
--- a/core/modules/system/tests/themes/test_theme_phptemplate/theme_test.template_test.tpl.php
+++ b/core/modules/system/tests/themes/test_theme_phptemplate/theme_test.template_test.tpl.php
@@ -1,2 +1,2 @@
 <!-- Output for Theme API test -->
-Success: Template overridden.
+<?php print 'Success: Template overridden.'; ?>
diff --git a/core/themes/engines/phptemplate/phptemplate.engine b/core/themes/engines/phptemplate/phptemplate.engine
index 88c09c7..718d460 100644
--- a/core/themes/engines/phptemplate/phptemplate.engine
+++ b/core/themes/engines/phptemplate/phptemplate.engine
@@ -23,3 +23,35 @@ function phptemplate_theme($existing, $type, $theme, $path) {
   $templates += drupal_find_theme_templates($existing, '.tpl.php', $path);
   return $templates;
 }
+
+/**
+ * Implements hook_extension().
+ */
+function phptemplate_extension() {
+  return '.tpl.php';
+}
+
+/**
+ * Renders a system default template, which is essentially a PHP template.
+ *
+ * @param $template_file
+ *   The filename of the template to render.
+ * @param $variables
+ *   A keyed array of variables that will appear in the output.
+ *
+ * @return
+ *   The output generated by the template.
+ */
+function phptemplate_render_template($template_file, $variables) {
+  // Extract the variables to a local namespace
+  extract($variables, EXTR_SKIP);
+
+  // Start output buffering
+  ob_start();
+
+  // Include the template file
+  include DRUPAL_ROOT . '/' . $template_file;
+
+  // End buffering and return its contents
+  return ob_get_clean();
+}