diff --git a/phpgwapi/inc/class.config.inc.php b/phpgwapi/inc/class.config.inc.php
index 1e4c59f114..6879a437ab 100755
--- a/phpgwapi/inc/class.config.inc.php
+++ b/phpgwapi/inc/class.config.inc.php
@@ -121,12 +121,12 @@ class config
 	 */
 	/* static */ function save_value($name,$value,$app=null)
 	{
-		if (!$app && !isset($this))
+		if (!$app && (!isset($this) || !is_a($this,__CLASS__)))
 		{
 			throw new egw_exception_assertion_failed('$app parameter required for static call of config::save_value($name,$value,$app)!');
 		}
 		//echo "<p>config::save_value('$name','".print_r($value,True)."','$app')</p>\n";
-		if (!$app || isset($this) && is_a($this,'config') && $app == $this->appname)
+		if (!$app || isset($this) && is_a($this,__CLASS__) && $app == $this->appname)
 		{
 			$this->config_data[$name] = $value;
 		}