diff --git a/tryton/gui/window/win_export.py b/tryton/gui/window/win_export.py
index a7eaecc618..636df5e75b 100644
--- a/tryton/gui/window/win_export.py
+++ b/tryton/gui/window/win_export.py
@@ -359,7 +359,7 @@ class WinExport(NoModal):
                             self.on_row_expanded(self.view1, iter,
                                     self.model1.get_path(iter))
                             iter = self.model1.iter_children(iter)
-                            prefix = parent + '/'
+                            prefix += parent + '/'
                             break
                         else:
                             iter = self.model1.iter_next(iter)