BUTTE, Mont. — A 27-year-old Montana man has pleaded guilty to shaking his 5-week-old son, causing severe brain injuries.

The Montana Standard reports (http://bit.ly/2wm3W5r ) Austin Blair Johnson of Butte entered a guilty plea Thursday at his arraignment on a charge of assault on a minor resulting in serious bodily injury. Defendants rarely plead guilty at arraignment.

The baby was taken to the hospital on July 1 with a head injury and transferred to Primary Care Children’s Hospital in Salt Lake City. Johnson eventually acknowledged being frustrated with the baby’s crying and shaking him.

Johnson has been jailed since July 12 and was returned to jail following his plea. District Judge Kurt Krueger has not scheduled a sentencing date.

Information from: The Montana Standard, http://www.mtstandard.com