diff --git a/accounts/doctype/sales_invoice/sales_invoice.py b/accounts/doctype/sales_invoice/sales_invoice.py
index a146e93..ef6f66c 100644
--- a/accounts/doctype/sales_invoice/sales_invoice.py
+++ b/accounts/doctype/sales_invoice/sales_invoice.py
@@ -719,7 +719,7 @@
 	if not day:
 		day = getdate(dt).day
 	if month > 12:
-		month, year = m-12, y+1
+		month, year = month-12, year+1
 	try:
 		next_month_date = datetime.date(year, month, day)
 	except:
@@ -909,4 +909,4 @@
 		webnotes.msgprint("Default Bank / Cash Account not set in Mode of Payment: %s. Please add a Default Account in Mode of Payment master." % mode_of_payment)
 	return {
 		"cash_bank_account": val
-	}
\ No newline at end of file
+	}