diff -u b/core/includes/module.inc b/core/includes/module.inc
--- b/core/includes/module.inc
+++ b/core/includes/module.inc
@@ -126,33 +126,20 @@
       return $lists['bootstrap'];
     }
     if ($cached = cache('bootstrap')->get('bootstrap_modules')) {
-      $bootstrap_list = $cached->data;
+      $lists['bootstrap'] = $cached->data;
       // To avoid a separate database lookup for the filepath, prime the
       // drupal_get_filename() static cache for bootstrap modules only.
       // The rest is stored separately to keep the bootstrap module cache small.
-      foreach ($bootstrap_list as $module => $filename) {
+      foreach ($lists['bootstrap'] as $module => $filename) {
         _system_list_warm('module', $module, $filename);
       }
     }
     else {
-      $enabled_modules = config('system.module')->get();
-      _system_list_warm('module', 'system', 'core/modules/system.module', TRUE);
-      $module_data = system_rebuild_module_data();
-      $bootstrap_list = array();
-      foreach ($enabled_modules as $module => $weight) {
-        $filename = $module_data[$module]->filename;
-        _system_list_warm('module', $module, $filename, TRUE);
-        foreach (bootstrap_hooks() as $hook) {
-          if (function_exists($module .'_' . $hook)) {
-            $bootstrap_list[$module] = $filename;
-          }
-        }
-      }
-      cache('bootstrap')->set('bootstrap_modules', $bootstrap_list);
+      $lists = _system_list_rebuild();
     }
     // We only return the module names here since module_list() doesn't need
     // the filename itself.
-    $lists['bootstrap'] = array_keys($bootstrap_list);
+    $lists['bootstrap'] = array_keys($lists['bootstrap']);
   }
   // Otherwise build the list for enabled modules and themes.
   elseif (!isset($lists['module_enabled'])) {
@@ -160,79 +147,8 @@
       $lists = $cached->data;
     }
     else {
-      // The module name (rather than the filename) is used as the fallback
-      // weighting in order to guarantee consistent behavior across different
-      // Drupal installations, which might have modules installed in different
-      // locations in the file system. The ordering here must also be
-      // consistent with the one used in module_implements().
-      $enabled_themes = config('system.theme')->get();
-      $enabled_modules = config('system.module')->get();
-      // It's important to retrieve these first because the rebuild calls
-      // reset the system_list static.
-      $bootstrap_list = $lists['bootstrap'];
-      _system_list_warm('module', 'system', 'core/modules/system.module', TRUE);
-      $module_data = system_rebuild_module_data();
-      $theme_data = system_rebuild_theme_data();
-      $lists = array(
-        'bootstrap' => $bootstrap_list,
-        'module_enabled' => array(),
-        'theme' => array(),
-        'filepaths' => array(),
-      );
-      foreach ($theme_data as $key => $theme) {
-        $lists['theme'][$key] = $theme;
-        $status = isset($enabled_themes[$key]);
-        $lists['theme'][$key]->status = $status;
-        $lists['theme'][$key]->name = $key;
-        // Build a list of filenames so drupal_get_filename can use it.
-        if ($status) {
-          $lists['filepaths'][] = array(
-            'type' => 'theme',
-            'name' => $key,
-            'filepath' => $theme->filename
-          );
-        }
-      }
-      foreach ($lists['theme'] as $key => $theme) {
-        if (!empty($theme->info['base theme'])) {
-          // Make a list of the theme's base themes.
-          require_once DRUPAL_ROOT . '/core/includes/theme.inc';
-          $lists['theme'][$key]->base_themes = drupal_find_base_themes($lists['theme'], $key);
-          // Don't proceed if there was a problem with the root base theme.
-          if (!current($lists['theme'][$key]->base_themes)) {
-            continue;
-          }
-          // Determine the root base theme.
-          $base_key = key($lists['theme'][$key]->base_themes);
-          // Add to the list of sub-themes for each of the theme's base themes.
-          foreach (array_keys($lists['theme'][$key]->base_themes) as $base_theme) {
-            $lists['theme'][$base_theme]->sub_themes[$key] = $lists['theme'][$key]->info['name'];
-          }
-          // Add the base theme's theme engine info.
-          $lists['theme'][$key]->info['engine'] = $lists['theme'][$base_key]->info['engine'];
-        }
-        else {
-          // A plain theme is its own base theme.
-          $base_key = $key;
-        }
-        // Set the theme engine prefix.
-        $lists['theme'][$key]->prefix = ($lists['theme'][$key]->info['engine'] == 'theme') ? $base_key : $lists['theme'][$key]->info['engine'];
-      }
-
-     foreach ($enabled_modules as $name => $weight) {
-        // Build a list of all enabled modules.
-        $lists['module_enabled'][$name] = $name;
-        // Build a list of filenames so drupal_get_filename can use it.
-        $lists['filepaths'][] = array(
-          'type' => 'module',
-          'name' => $name,
-          'filepath' => $module_data[$name]->filename,
-        );
-      }
-      cache('bootstrap')->set('system_list', $lists);
+      $lists = _system_list_rebuild();
     }
-    // To avoid a separate database lookup for the filepath, prime the
-    // drupal_get_filename() static cache with all enabled modules and themes.
     foreach ($lists['filepaths'] as $item) {
       _system_list_warm($item['type'], $item['name'], $item['filepath']);
     }
@@ -242,6 +158,88 @@
 }
 
 /**
+ * Rebuild the system list data structure.
+ */
+function _system_list_rebuild() {
+  // The module name (rather than the filename) is used as the fallback
+  // weighting in order to guarantee consistent behavior across different
+  // Drupal installations, which might have modules installed in different
+  // locations in the file system. The ordering here must also be
+  // consistent with the one used in module_implements().
+  $enabled_themes = config('system.theme')->get();
+  $enabled_modules = config('system.module')->get();
+  _system_list_warm('module', 'system', 'core/modules/system.module', TRUE);
+  $module_data = system_rebuild_module_data(FALSE);
+  $theme_data = system_rebuild_theme_data(FALSE);
+  $lists = array(
+    'bootstrap' => array(),
+    'module_enabled' => array(),
+    'theme' => array(),
+    'filepaths' => array(),
+  );
+  foreach ($theme_data as $key => $theme) {
+    $lists['theme'][$key] = $theme;
+    $status = isset($enabled_themes[$key]);
+    $lists['theme'][$key]->status = $status;
+    $lists['theme'][$key]->name = $key;
+    // Build a list of filenames so drupal_get_filename can use it.
+    if ($status) {
+      $lists['filepaths'][] = array(
+        'type' => 'theme',
+        'name' => $key,
+        'filepath' => $theme->filename
+      );
+    }
+  }
+  foreach ($lists['theme'] as $key => $theme) {
+    if (!empty($theme->info['base theme'])) {
+      // Make a list of the theme's base themes.
+      require_once DRUPAL_ROOT . '/core/includes/theme.inc';
+      $lists['theme'][$key]->base_themes = drupal_find_base_themes($lists['theme'], $key);
+      // Don't proceed if there was a problem with the root base theme.
+      if (!current($lists['theme'][$key]->base_themes)) {
+        continue;
+      }
+      // Determine the root base theme.
+      $base_key = key($lists['theme'][$key]->base_themes);
+      // Add to the list of sub-themes for each of the theme's base themes.
+      foreach (array_keys($lists['theme'][$key]->base_themes) as $base_theme) {
+        $lists['theme'][$base_theme]->sub_themes[$key] = $lists['theme'][$key]->info['name'];
+      }
+      // Add the base theme's theme engine info.
+      $lists['theme'][$key]->info['engine'] = $lists['theme'][$base_key]->info['engine'];
+    }
+    else {
+      // A plain theme is its own base theme.
+      $base_key = $key;
+    }
+    // Set the theme engine prefix.
+    $lists['theme'][$key]->prefix = ($lists['theme'][$key]->info['engine'] == 'theme') ? $base_key : $lists['theme'][$key]->info['engine'];
+  }
+
+ foreach ($enabled_modules as $name => $weight) {
+    // Build a list of all enabled modules.
+    $lists['module_enabled'][$name] = $name;
+    $filename = $module_data[$name]->filename;
+    // Build a list of filenames so drupal_get_filename can use it.
+    $lists['filepaths'][] = array(
+      'type' => 'module',
+      'name' => $name,
+      'filepath' => $filename,
+    );
+    _system_list_warm('module', $name, $filename, TRUE);
+    foreach (bootstrap_hooks() as $hook) {
+      if (function_exists($name .'_' . $hook)) {
+        $lists['bootstrap'][] = $filename;
+      }
+    }
+  }
+  cache('bootstrap')->set('system_list', $lists);
+  cache('bootstrap')->set('bootstrap_modules', $lists['bootstrap']);
+  return $lists;
+}
+
+/**
  * Prepares a module for loading and optionally calls drupal_load().
  *
  * @param string $type
diff -u b/core/modules/system/system.module b/core/modules/system/system.module
--- b/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -2780,7 +2780,7 @@
  * @return
  *   Array of all available modules and their data.
  */
-function system_rebuild_module_data() {
+function system_rebuild_module_data($reset = TRUE) {
   $modules_cache = &drupal_static(__FUNCTION__, array());
   // Only rebuild once per request. $modules and $modules_cache cannot be
   // combined into one variable, because the $modules_cache variable is reset by
@@ -2803,7 +2803,9 @@
     }
     // As noted above, system_list_reset() deletes $modules_cache so the order
     // here is important.
-    system_list_reset();
+    if ($reset) {
+      system_list_reset();
+    }
     $modules_cache['data'] = $modules;
   }
   // Running the info alter function is not possible before full bootstrap.
@@ -2970,14 +2972,16 @@
  * @return
  *   Array of all available themes and their data.
  */
-function system_rebuild_theme_data() {
+function system_rebuild_theme_data($reset = TRUE) {
   $themes = _system_rebuild_theme_data();
   ksort($themes);
   $themes_status = config('system.theme')->get();
   foreach ($themes as $theme => $data) {
     $data->status = isset($themes_status[$theme]);
   }
-  system_list_reset();
+  if ($reset) {
+    system_list_reset();
+  }
   return $themes;
 }