diff --git a/app/db/sql_sentences.py b/app/db/sql_sentences.py
index 1d49bc0..e6f4907 100644
--- a/app/db/sql_sentences.py
+++ b/app/db/sql_sentences.py
@@ -40,7 +40,7 @@ INSERT_INVOICE = (
     "SELECT "
     "%s AS id, "
     "%s AS company_id, "
-    "COALESCE(MAX(invoice_number + 0),0)+1 AS invoice_number, "
+    "LPAD((COALESCE(MAX(invoice_number), 0) + 1), 3, '0') AS invoice_number,"
     "%s AS status, %s AS is_proforma, %s AS series, %s AS reference, %s AS invoice_date, %s AS operation_date, %s AS description, %s AS notes, "
     "%s AS subtotal_amount_value, %s AS discount_amount_value, %s AS discount_percentage_value, %s AS taxable_amount_value, %s AS taxes_amount_value, %s AS total_amount_value, "
     "%s AS customer_id, %s AS customer_tin, %s AS customer_name, %s AS customer_street, %s AS customer_city, %s AS customer_province, %s AS customer_postal_code, %s AS customer_country, "