diff --git a/app/models/invoice.rb b/app/models/invoice.rb
index 002d124d3..effefc3b9 100644
--- a/app/models/invoice.rb
+++ b/app/models/invoice.rb
@@ -8,7 +8,7 @@ class Invoice < ActiveRecord::Base
   accepts_nested_attributes_for :invoice_items
 
   attr_accessor :billing_email
-  validates :billing_email, format: { with: /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i }
+  validates :billing_email, format: { with: /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i }, allow_blank: true
 
   validates :invoice_type, :due_date, :currency, :seller_name,
             :seller_iban, :buyer_name, :invoice_items, :vat_prc, presence: true