A Slovenian opera singer undergoing surgery for a brain tumor remained awake so doctors could ensure he would maintain his ability to sing, Metro.co.uk reported.

As doctors worked on Ambroz Bajec-Lapajn’s exposed brain on June 13, 2014, they encouraged him to talk and sing.

A Youtube video of the surgery shows the professional tenor talking with the surgery team and singing Franz Schubert’s “Gute Nacht” during the procedure at the University Medical Center Utrecht in the Netherlands. He was asked to sing from the minor to major key to see if he could recognize the key change, according to his video. At  the 2:40 mark, he appears to lose his ability to sing, but smiles after encouragement from the team and resumes singing. Toward the end of the video, doctors ask him to touch individual fingers to his thumb.

“It’s been more than a year since [the operation], and I’m doing fine, continuing my professional singing career,” Bajec-Lapajne wrote on his YouTube video posting.