=== modified file 'includes/common.inc'
--- includes/common.inc	
+++ includes/common.inc	
@@ -1704,23 +1704,22 @@ function drupal_cron_run() {
   }
 
   // Check if the last cron run completed
-  if (variable_get('cron_busy', FALSE)) {
+  if (variable_get('cron_start', FALSE) + 240 > time()) {
     watchdog('cron', t('Last cron run did not complete.'), WATCHDOG_WARNING);
   }
   else {
-    variable_set('cron_busy', TRUE);
-  }
-
-  // Iterate through the modules calling their cron handlers (if any):
-  module_invoke_all('cron');
+    variable_set('cron_start', time());
+    // Iterate through the modules calling their cron handlers (if any):
+    module_invoke_all('cron');
+
+    // Clean up
+    variable_set('cron_start', 0);
+    variable_set('cron_last', time());
+    watchdog('cron', t('Cron run completed.'), WATCHDOG_NOTICE);
 
-  // Clean up
-  variable_set('cron_busy', FALSE);
-  variable_set('cron_last', time());
-  watchdog('cron', t('Cron run completed.'), WATCHDOG_NOTICE);
-
-  // Return TRUE so other functions can check if it did run successfully
-  return TRUE;
+    // Return TRUE so other functions can check if it did run successfully
+    return TRUE;
+  }
 }
 
 /**