diff --git a/juggl-server/api/services/dbOperations.inc.php b/juggl-server/api/services/dbOperations.inc.php
index 16ee546..cff258f 100644
--- a/juggl-server/api/services/dbOperations.inc.php
+++ b/juggl-server/api/services/dbOperations.inc.php
@@ -201,7 +201,7 @@ class DbOperations
     function innerJoin(string $table, string $externAttribute, string $internAttribute = "", string $internTable = "")
     {
         if ($internTable === "") {
-            $internTable = substr($this->table, sizeof($this->tablePrefix));
+            $internTable = substr($this->table, strlen($this->tablePrefix));
         }
         if ($internAttribute === "") {
             $internAttribute = $externAttribute;