diff --git a/core/lib/Drupal/Core/Theme/Registry.php b/core/lib/Drupal/Core/Theme/Registry.php
index c19fd4d..de9ca4a 100644
--- a/core/lib/Drupal/Core/Theme/Registry.php
+++ b/core/lib/Drupal/Core/Theme/Registry.php
@@ -507,12 +507,14 @@ protected function processExtension(array &$cache, $name, $type, $theme, $path)
           $prefixes = array();
 
           if ($type == 'module') {
-            // Default variable preprocessor prefix.
-            $prefixes[] = 'template';
+            // Modules may implement the default preprocessor of a hook.
+            if (function_exists('template_preprocess_' . $hook)) {
+              $info['preprocess functions'][] = 'template_preprocess_' . $hook;
+            }
             // Add all modules so they can intervene with their own variable
             // preprocessors. This allows them to provide variable preprocessors
             // even if they are not the owner of the current hook.
-            $prefixes = array_merge($prefixes, $module_list);
+            $prefixes = $module_list;
           }
           elseif ($type == 'theme_engine' || $type == 'base_theme_engine') {
             // Theme engines get an extra set that come before the normally
diff --git a/core/lib/Drupal/Core/Theme/ThemeManager.php b/core/lib/Drupal/Core/Theme/ThemeManager.php
index ea764a7..342eec0 100644
--- a/core/lib/Drupal/Core/Theme/ThemeManager.php
+++ b/core/lib/Drupal/Core/Theme/ThemeManager.php
@@ -288,11 +288,13 @@ public function render($hook, array $variables) {
       }
     }
 
-    // Set default variables before preprocess hooks.
-    $this->addDefaultTemplateVariables($variables);
-    $render_element_type = isset($info['render element']) ? $info['render element'] : NULL;
-    $this->addElementAttributeVariables($variables, $render_element_type);
-
+    // Don't add template variables for hooks implemented as functions.
+    if (!isset($info['function'])) {
+      // Set default variables before preprocess hooks.
+      $this->addDefaultTemplateVariables($variables);
+      $render_element_type = isset($info['render element']) ? $info['render element'] : NULL;
+      $this->addElementAttributeVariables($variables, $render_element_type);
+    }
     // Invoke preprocess hooks.
     // By default $info['preprocess functions'] should always be set, but it's
     // good to check it if default Registry service implementation is