THE HAGUE, Netherlands (AP) — International judges on Wednesday postponed an appeal hearing for former Bosnian Serb military chief Ratko Mladic against his convictions on charges including genocide because Mladic is due to undergo surgery.

The hearing had been scheduled for March 17-18 at the International Residual Mechanism for Criminal Tribunals, a court that handles appeals and other cases from the now closed U.N. war crimes tribunals for the former Yugoslavia and Rwanda.

Mladic was given a life sentence on Nov. 22, 2017, after being convicted of crimes including genocide for leading troops who massacred more than 8,000 Muslim men and boys at the Srebrenica enclave in Bosnia in 1995.

He appealed and remains in custody in The Hague. Prosecutors also have appealed because Mladic was acquitted of a second count of genocide and they want that acquittal overturned.

According to filings released Wednesday by the residual mechanism, Mladic is to undergo surgery to remove a benign polyp from his colon.

Judges didn’t set a new date for the hearing, but indicated they want to hold it about six weeks after Mladic’s surgery.

Mladic, who turns 78 on Thursday, has been in frail health for years.