diff --git a/django_lostplaces/lostplaces/forms.py b/django_lostplaces/lostplaces/forms.py
index a770ef2..b391316 100644
--- a/django_lostplaces/lostplaces/forms.py
+++ b/django_lostplaces/lostplaces/forms.py
@@ -26,7 +26,7 @@ class ExplorerCreationForm(UserCreationForm):
             self.add_error('voucher', 'Invalid voucher')
             return False
 
-        if not fetched_voucher.valid:
+        if not fetched_voucher.valid():
             self.add_error('voucher', 'Expired voucher')
             return False