diff --git a/admin/include/updates.class.php b/admin/include/updates.class.php
index 726f27b1c..be016196c 100644
--- a/admin/include/updates.class.php
+++ b/admin/include/updates.class.php
@@ -56,14 +56,14 @@ class updates
 
   static function check_piwigo_upgrade()
   {
-    $_SESSION['need_update'] = null;
+    $_SESSION['need_update'.PHPWG_VERSION] = null;
 
     if (preg_match('/(\d+\.\d+)\.(\d+)/', PHPWG_VERSION, $matches)
       and @fetchRemote(PHPWG_URL.'/download/all_versions.php?rand='.md5(uniqid(rand(), true)), $result))
     {
       $all_versions = @explode("\n", $result);
       $new_version = trim($all_versions[0]);
-      $_SESSION['need_update'] = version_compare(PHPWG_VERSION, $new_version, '<');
+      $_SESSION['need_update'.PHPWG_VERSION] = version_compare(PHPWG_VERSION, $new_version, '<');
     }
   }
 
@@ -610,7 +610,6 @@ class updates
             deltree(PHPWG_ROOT_PATH.$conf['data_location'].'update');
             invalidate_user_cache(true);
             $template->delete_compiled_templates();
-            unset($_SESSION['need_update']);
             if ($step == 2)
             {
               $page['infos'][] = l10n('Update Complete');
diff --git a/include/ws_functions/pwg.extensions.php b/include/ws_functions/pwg.extensions.php
index 23685b4dd..523324d57 100644
--- a/include/ws_functions/pwg.extensions.php
+++ b/include/ws_functions/pwg.extensions.php
@@ -309,12 +309,12 @@ function ws_extensions_checkupdates($params, $service)
   $update = new updates();
   $result = array();
 
-  if (!isset($_SESSION['need_update']))
+  if (!isset($_SESSION['need_update'.PHPWG_VERSION]))
   {
     $update->check_piwigo_upgrade();
   }
 
-  $result['piwigo_need_update'] = $_SESSION['need_update'];
+  $result['piwigo_need_update'] = $_SESSION['need_update'.PHPWG_VERSION];
 
   $conf['updates_ignored'] = unserialize($conf['updates_ignored']);