Index: modules/update/update.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/update/update.module,v
retrieving revision 1.17
diff -u -p -r1.17 update.module
--- modules/update/update.module	30 Jan 2008 10:14:42 -0000	1.17
+++ modules/update/update.module	23 Sep 2008 10:17:02 -0000
@@ -286,7 +286,9 @@ function _update_requirement_check($proj
 function update_cron() {
   $frequency = variable_get('update_check_frequency', 1);
   $interval = 60 * 60 * 24 * $frequency;
-  if (time() - variable_get('update_last_check', 0) > $interval) {
+  // Cron should check for updates if there is no update data cached or if the configured
+  // update interval has elapsed.
+  if (!cache_get('update_info', 'cache_update') || ((time() - variable_get('update_last_check', 0)) > $interval)) {
     update_refresh();
     _update_cron_notify();
   }