A Customs review of its response to the capsize of an asylum seeker boat in which two people died says minor changes should be made to boarding practices.

However, it also says these improvements could not have prevented the tragedy which occurred on March 25 near Christmas Island.

That day, the Customs vessel Ocean Protector went to the boat carrying 96 people.

Two officers boarded, but the vessel rolled when it was struck by two large waves.

Customs rescued people from the water, but two - a woman and a boy - were believed drowned.

"This was a tragic event," Customs and Border Protection said in a statement on Wednesday.

Later, Customs began an assessment to see if procedures were followed and if there could be improvement.

Among the findings - which won't be publicly released for security reasons - were proposals for minor refinements to boarding practices and ongoing support to personnel involved in critical incidents.

"In light of the findings and sequence of events, the minor improvements would not have impacted the outcome of this particular incident," Customs concluded.

Information gathered during the assessment will be available to any police investigations or coronial processes.