--- poormanscron.module.orig	2008-12-19 15:59:28.000000000 -0500
+++ poormanscron.module	2008-12-19 16:01:03.000000000 -0500
@@ -29,7 +29,12 @@ function poormanscron_help($path, $arg) 
 function poormanscron_exit() {
 
   // Calculate when the next poormanscron run is due.
-  $lastrun = variable_get('poormanscron_lastrun', 0);
+  $lastrun = 0;
+  db_lock_table('variable');
+  $result = db_query("SELECT * FROM {variable} where name = 'poormanscron_lastrun'");
+  while ($variable = db_fetch_object($result)) {
+    $lastrun = unserialize($variable->value);
+  }
   $nextrun = $lastrun + 60 * variable_get('poormanscron_interval', 60);
 
   // If the configured time has passed, start the next poormanscron run.
@@ -38,6 +43,7 @@ function poormanscron_exit() {
     // If this cron run fails to complete, wait a few minutes before retrying.
     variable_set('poormanscron_lastrun',
        $lastrun + 60 * variable_get('poormanscron_retry_interval', 10));
+    db_unlock_tables();
 
     // Get the current Drupal messages. Use drupal_set_message() so that
     // the messages aren't deleted in case the cron run fails and
@@ -87,6 +93,8 @@ function poormanscron_exit() {
         }
       }
     }
+  } else {
+    db_unlock_tables();
   }
 }