diff --git a/purchase.py b/purchase.py
index dd4356a679..1ce9abbf64 100644
--- a/purchase.py
+++ b/purchase.py
@@ -1643,10 +1643,8 @@ class Invoice(OSV):
     def __init__(self):
         super(Invoice, self).__init__()
         self._error_messages.update({
-            'delete_purchase_invoice': 'You can not delete invoices ' \
+                'delete_purchase_invoice': 'You can not delete invoices ' \
                     'that comes from a purchase!',
-            })
-        self._error_messages.update({
                 'reset_invoice': 'You cannot reset to draft an invoice '\
                     'generated by a purchase.',
             })