Index: modules/filter/filter.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/filter/filter.module,v
retrieving revision 1.239
diff -u -p -r1.239 filter.module
--- modules/filter/filter.module	30 Dec 2008 16:43:17 -0000	1.239
+++ modules/filter/filter.module	4 Jan 2009 20:23:54 -0000
@@ -452,9 +452,9 @@ function check_markup($text, $format = F
       $text = module_invoke($filter->module, 'filter', 'process', $filter->delta, $format, $text, $langcode, $cache_id);
     }
 
-    // Store in cache with a minimum expiration time of 1 day.
+    // Store in cache using the system's expiration time or an expiration time of 1 days if it is not set.
     if ($cache) {
-      cache_set($cache_id, $text, 'cache_filter', REQUEST_TIME + (60 * 60 * 24));
+      cache_set($cache_id, $text, 'cache_filter', REQUEST_TIME + variable_get('cache_lifetime', 86400));
     }
   }
   else {