diff --git a/php/define.php b/php/define.php
index a215adc..d7bebb7 100644
--- a/php/define.php
+++ b/php/define.php
@@ -26,7 +26,7 @@ define('LYCHEE_URL_UPLOADS_BIG', 'uploads/big/');
 define('LYCHEE_URL_UPLOADS_MEDIUM', 'uploads/medium/');
 define('LYCHEE_URL_UPLOADS_THUMB', 'uploads/thumb/');
 
-function defineTablePrefix($dbTablePrefix = '') {
+function defineTablePrefix($dbTablePrefix) {
 
 	// This part is wrapped into a function, because it needs to be called
 	// after the config-file has been loaded. Other defines are available
@@ -34,6 +34,7 @@ function defineTablePrefix($dbTablePrefix = '') {
 
 	// Parse table prefix
 	// Old users do not have the table prefix stored in their config-file
+	if (isset($dbTablePrefix)===false) $dbTablePrefix = '';
 	if ($dbTablePrefix!=='') $dbTablePrefix .= '_';
 
 	// Define tables