diff --git a/db_backend.php b/db_backend.php
index 6876558..182a1c7 100644
--- a/db_backend.php
+++ b/db_backend.php
@@ -65,6 +65,17 @@
         }
     }
 
+    function updateInvoice($user) {
+        $this->log->debug("updateInvoice");
+        $sql = "UPDATE person SET invoice = :invoice WHERE id = :id;";
+        $stmt = $this->pdo->prepare($sql);
+
+        $stmt->bindParam(':invoice', $user->invoice, PDO::PARAM_LOB);
+        $stmt->bindParam(':id', $user->id);
+
+        return $stmt->execute();
+    }
+
     function mail_count($email)
     {
         $sql = "SELECT COUNT(*) FROM person WHERE email = :email";