Foreign exchange difference

Our client makes remittances to a non-resident (Professionals) and we are liable to deduct tax for the same. There are three exchange rates to be considered namely date of invoice, Form 15CB date and the actual date of remittance. We have passed the journal on the date of invoice considering the exchange rate as on that date and the foreign exchange gain/loss is calculated by taking the difference between the exchange rate as on the invoice date and date of actual remittance. Our doubt is regarding the treatment of exchange difference arising in the TDS amount. Please clarify the same.