diff --git includes/module.inc includes/module.inc
index e6ae4c7..b7b20cf 100644
--- includes/module.inc
+++ includes/module.inc
@@ -336,6 +336,8 @@ function module_enable($module_list, $enable_dependencies = TRUE, $disable_modul
 
   $invoke_modules = array();
 
+  // Required for _drupal_install_module.
+  include_once DRUPAL_ROOT . '/includes/install.inc'
   // Try to install the enabled modules and collect which were installed.
   // $module_list is not changed and already installed modules are ignored.
   $modules_installed = array_filter($module_list, '_drupal_install_module');