diff --git a/wizard_runreport.py b/wizard_runreport.py
index d8d5c5e..a372ee5 100644
--- a/wizard_runreport.py
+++ b/wizard_runreport.py
@@ -125,7 +125,7 @@ class RunXRechnungReport(Wizard):
     def do_export(self, action):
         """ run export
         """
-        if self.start.state not in {'paid', 'posted'}:
+        if self.start.state not in ['paid', 'posted']:
             raise UserError(gettext(
                 'account_invoice_xrechnung.msg_invoice_must_posted',
                 invname=self.start.invoice.rec_name))