diff --git a/membershipworks/forms.py b/membershipworks/forms.py
index 8655ba8..29789ab 100644
--- a/membershipworks/forms.py
+++ b/membershipworks/forms.py
@@ -22,7 +22,7 @@ class EventInvoiceForm(forms.Form):
         super().__init__(*args, **kwargs)
 
     def clean(self):
-        if hasattr(self.event, "invoice") is not None:
+        if hasattr(self.event, "invoice"):
             raise forms.ValidationError("An invoice was already created!")
 
         if not self.event.ready_for_invoice: