diff --git a/includes/bootstrap.inc b/includes/bootstrap.inc
index 3693719f1595..ba88daf7b417 100644
--- a/includes/bootstrap.inc
+++ b/includes/bootstrap.inc
@@ -1663,8 +1663,13 @@ function drupal_get_schema($table = NULL, $rebuild = FALSE) {
  */
 function drupal_function_exists($function) {
   static $checked = array();
+  static $maintenance;
 
-  if (defined('MAINTENANCE_MODE')) {
+  if (!isset($maintenance)) {
+    $maintenance = defined('MAINTENANCE_MODE');
+  }
+
+  if ($maintenance) {
     return function_exists($function);
   }