Judge Ronald Giles rejected a prosecution move, agreeing with the mayor's attorneys that a no-contact order didn't include Ayanna Kilpatrick. The mayor had spent time with his sister during the weekend.
"I don't see the issue," the judge said. "I really don't. There isn't an issue."
Last week, Giles had sent the mayor to jail overnight in a separate perjury case after learning he had traveled to Windsor, Ontario, in July without notifying authorities, a condition of his release on bail.
Kilpatrick was released Friday.
That same day, the mayor was charged with assaulting two investigators who were trying to deliver a subpoena at his sister's house in July in the perjury case.
The state attorney general's office said in a court filing that the mayor had been ordered to have no contact with witnesses in the assault case.
Prosecutors said Kilpatrick violated that condition because he and Ayanna Kilpatrick were together Saturday at the home of their mother, U.S. Rep. Carolyn Cheeks Kilpatrick, D-Mich.
The defense said Magistrate Renee McDuffee had clarified Friday that Kilpatrick could have contact with his sister.
Giles said Tuesday the no-contact order was for the two investigators involved in the altercation.