diff --git a/inc/tz/updatecheck.php b/inc/tz/updatecheck.php
index 2d0ed736..d751f633 100644
--- a/inc/tz/updatecheck.php
+++ b/inc/tz/updatecheck.php
@@ -10,6 +10,8 @@
 */
 
 require_once('vCalendar.php');
+require_once('XMLDocument.php');
+require_once('RRule-v2.php');
 
 $new_zones = 0;
 $modified_zones = 0;
@@ -17,6 +19,107 @@ $modified_zones = 0;
 if ( empty($c->tzsource) ) $c->tzsource = '../zonedb/vtimezones';
 if ( preg_match('{^http}', $c->tzsource ) ) {
 
+  function fetch_tz_ids( $base_url, $current_zones ) {
+    global $request;
+    $result = array();
+    $list_url = $base_url . '?action=list';
+    printf( "Fetching timezone list\n", $list_url );  
+    $raw_xml = file_get_contents($list_url);
+    $xml_parser = xml_parser_create_ns('UTF-8');
+    $xml_tags = array();
+    xml_parser_set_option ( $xml_parser, XML_OPTION_SKIP_WHITE, 1 );
+    xml_parser_set_option ( $xml_parser, XML_OPTION_CASE_FOLDING, 0 );
+    $rc = xml_parse_into_struct( $xml_parser, $raw_xml, $xml_tags );
+    if ( $rc == false ) {
+      dbg_error_log( 'ERROR', 'XML parsing error: %s at line %d, column %d', xml_error_string(xml_get_error_code($xml_parser)),
+                  xml_get_current_line_number($xml_parser), xml_get_current_column_number($xml_parser) );
+      $request->PreconditionFailed(400, 'invalid-xml',
+                  sprintf('XML parsing error: %s at line %d, column %d', xml_error_string(xml_get_error_code($xml_parser)),
+                  xml_get_current_line_number($xml_parser), xml_get_current_column_number($xml_parser) ));
+    }
+    xml_parser_free($xml_parser);
+    $position = 0;
+    $xmltree = BuildXMLTree( $xml_tags, $position);
+    $zones = $xmltree->GetElements('urn:ietf:params:xml:ns:timezone-service:summary');
+    foreach( $zones AS $zone ) {
+      $elements = $zone->GetElements('urn:ietf:params:xml:ns:timezone-service:tzid');
+      $tzid = $elements[0]->GetContent();
+      $elements = $zone->GetElements('urn:ietf:params:xml:ns:timezone-service:last-modified');
+      $last_modified = new RepeatRuleDateTime($elements[0]->GetContent());
+      if ( $last_modified > $current_zones[$tzid] ) {
+        $result[] = $tzid;
+        printf("Found timezone %s needs updating\n", $tzid);
+      }
+      $elements = $zone->GetElements('urn:ietf:params:xml:ns:timezone-service:alias');
+      foreach( $elements AS $element ) {
+        $alias = $element->GetContent();
+      }
+    }
+    return $result;
+  }
+
+  $changesince = null;
+  $qry = new AwlQuery("SELECT tzid, to_char(last_modified,'YYYY-MM-DD\"T\"HH24:MI:SS') AS last_modified FROM timezones");
+  $current_zones = array();
+  if ( $qry->Exec('tz/updatecheck',__LINE__,__FILE__) && $qry->rows() > 0 ) {
+    $row = $qry->Fetch();
+    $current_zones[$row->tzid] = new RepeatRuleDateTime($row->last_modified);
+  }
+  foreach( fetch_tz_ids($c->tzsource, $current_zones) AS $tzid ) {
+    $tz_url = $c->tzsource . '?action=get&tzid=' .$tzid;
+    $tzrow = null;
+    if ( $qry->QDo('SELECT * FROM timezones WHERE tzid=:tzid', array(':tzid' => $tzid)) && $qry->rows() > 0 ) {
+      $tzrow = $qry->Fetch();
+    }
+    printf( "Fetching zone for %s from %s\n", $tzid, $tz_url );  
+    dbg_error_log( 'tz/updatecheck', "Fetching zone for %s from %s\n", $tzid, $tz_url );  
+    $vtimezone = file_get_contents( $tz_url );
+    if ( empty($vtimezone) ) {
+      dbg_error_log('tz/updatecheck', 'Skipping zone "%s" - no data from server', $tzid );
+      continue;
+    }
+    if ( $vtimezone == $tzrow->vtimezone ) {
+      dbg_error_log('tz/updatecheck', 'Skipping zone "%s" - no change', $tzid );
+      continue;
+    }
+    $vtz = new vCalendar($vtimezone);
+    $last_modified = $vtz->GetPValue('LAST-MODIFIED');
+    if ( empty($last_modified) ) {
+      $last_modified = gmdate('Ymd\THis\Z');
+      // Then it was probably that way when we last updated the data, too :-(
+      if ( !empty($tzrow) ) {
+        $old_vtz = new vCalendar($tzrow->vtimezone);
+        $old_vtz->ClearProperties('LAST-MODIFIED');
+        // We need to add & remove this property so the Render is equivalent.
+        $vtz->AddProperty('LAST-MODIFIED',$last_modified);
+        $vtz->ClearProperties('LAST-MODIFIED');
+        if ( $vtz->Render() == $old_vtz->Render() ) {
+          dbg_error_log('tz/updatecheck', 'Skipping zone "%s" - no change', $tzid );
+          continue;
+        }
+      }
+      $vtz->AddProperty('LAST-MODIFIED',$last_modified);
+    }
+    dbg_error_log('tz/updatecheck', 'Writing %s zone for "%s"', (empty($tzrow)?"new":"updated"), $tzid );
+    $params = array(
+      ':tzid'           => $tzid,
+      ':olson_name'     => $tzid,
+      ':vtimezone'      => $vtz->Render(),
+      ':last_modified'  => $last_modified,
+      ':etag'			=> md5($vtz->Render())
+    );
+    if ( empty($tzrow) ) {
+      $new_zones++;
+      $sql = 'INSERT INTO timezones(tzid,active,olson_name,last_modified,etag,vtimezone) ';
+      $sql .= 'VALUES(:tzid,TRUE,:olson_name,:last_modified,:etag,:vtimezone)';
+    }
+    else {
+      $modified_zones++;
+      $sql = 'UPDATE timezones SET active=TRUE, olson_name=:olson_name, last_modified=:last_modified, ';
+      $sql .= 'etag=:etag, vtimezone=:vtimezone WHERE tzid=:tzid';
+    }
+    $qry->QDo($sql,$params);
+  }
 }
 else if ( file_exists($c->tzsource) ) {
   /**
@@ -90,11 +193,12 @@ else if ( file_exists($c->tzsource) ) {
     }
     $qry->QDo($sql,$params);
   }
-  header('Content-type: text/plain');
-  printf('Added %d new zones and updated data for %d zones', $new_zones, $modified_zones);
 }
 else {
   dbg_error_log('ERROR', '$c->tzsource is not configured to a good source of timezone data');
 }
 
+header('Content-type: text/plain');
+printf("Added %d new zones and updated data for %d zones\n", $new_zones, $modified_zones);
+
 exit(0);
\ No newline at end of file