The Defence Ministry says its project to upgrade the country's two frigates is within Cabinet's approved budget of $594m.
Allowances for foreign exchange movements appeared to push that up to almost $640m.
But Defence said this was a "technical adjustment" that did not add to the project's cash costs.
"Project costs are hedged and the cash costs for the project is forecasted to be within the Cabinet budget of $594 million," a spokesperson said.
An extra $150m had to be stumped up in 2017 to get new combat system equipment installed in Canada, on the Te Kaha and Te Mana.
The project agreed eight years ago, is almost at an end with the second of the two frigates due to leave Canada soon.
Defence said it expected to use the frigates until the mid-2030s.
