Halloween is a time for parties, dressing up and trick or treating – however, it’s unfortunately also a time when some people get their costumes wrong and can cause offence.

This is what Chris Hemsworth is taking a stand against, and he’s doing it in a pretty brave way.

He posted this picture on Instagram on Thursday as a show of solidarity with the protesters of the Standing Rock pipeline. The Standing Rock Sioux tribe is attempting to stop plans for the Dakota Access Pipeline to be built across their reservation, saying it will destroy indigenous burial grounds and contaminate their only water source. So far over 100 people have been arrested in the protest.

He uses the post to make a pretty powerful point about cultural appropriation, calling himself out on his own ignorance.

Chris says in the post: “I would also like to take this opportunity to raise something that has been bothering me for sometime. Last New Year’s Eve I was at a ‘Lone Ranger’ themed party where some of us, myself included, wore the traditional dress of First Nations people.

“I was stupidly unaware of the offence this may have caused and the sensitivity around this issue. I sincerely and unreservedly apologise to all First Nations people for this thoughtless action.

“I now appreciate that there is a great need for a deeper understanding of the complex and extensive issues facing indigenous communities. I hope that in highlighting my own ignorance I can help in some small way.”