Twitter boss Jack Dorsey said it never should have been possible for an employee to deactivate the account of President Donald Trump earlier this month.

The president’s account on Nov. 2 went dark for 11 minutes, during which his profile could not be searched and all of his tweets had disappeared.

At the time, Twitter said that the account “was inadvertently deactivated due to human error by a Twitter employee.” But it was later discovered that a rogue employee had taken it down on his or her last day of work.

At a Thursday conference sponsored by Dealbook, Dorsey said Twitter should have been able to prevent the prank.

“We started looking into the controls we have in place, what we can improve and where we have weaknesses, where we have gaps,” Dorsey said in an interview. “Second, particular policies around what agents have control over and what they don’t.”

Twitter has been making headlines for all the wrong reasons in the past few months, most recently having to freeze its verification process after verifying the account of Jason Kessler, who organized the neo-Nazi rally in Charlottesville, NC.

“Verification was meant to authenticate identity & voice but it is interpreted as an endorsement or an indicator of importance,” Twitter said after the incident. “We recognize that we have created this confusion and need to resolve it.”