When the experienced centre-back signed for the Sky Blues in January it was reported the deal involved the rest of this season, plus an option for next season.
The World Game understands Buijs had to play 10 games to trigger the extra year.
The 28-year-old had played nine games ahead of the last round of the regular season and was scheduled to rack up his 10th in the match with Newcastle Jets at Allianz Stadium on Saturday night.
Buijs was brought into the Sydney squad to replace Matthew Jurman, who departed the Sky Blues in early January to join Korean club Suwon Bluewings.
He has been very impressive as a partner for Alex Wilkinson in the heart of the defence as Sydney ran away with the Premier's Plate.
The Sky Blues brains trust, led by coach Graham Arnold, is known to be very happy with Buijs's contribution and Buijs has made it clear he enjoys playing for Sydney.
In an interview with The World Game on Thursday, Buijs said that when he arrived at the club his new teammates welcomed him straight in.
"From the first day I saw they were very positive and maybe because of that spirit they were unbeaten at the time," he said.
"It was easy to come into this team - they accept you, they talk with you and they help you."
Buijs said Arnold had done a lot to help him fit into the team structure and adapt to their playing style.
"I've been here for three months now and playing for nine weeks and things need to grow and I think that's happening with the players, the staff and the physio and medical side of it," he said.
"Graham helps me a lot to grow into the team and I appreciate that a lot."
Sydney were keen on central defender Rhys Williams when it seemed there might be a split between him and Perth Glory at the same time Jurman was leaving Sydney.
Buijs has since filled that hole in the team and Sydney want to keep all of their established defenders.
Competition for centre-back spots will only increase next season, with Seb Ryall back fit after missing most of this season through injury and young Aaron Calver more experienced.
Ryall and Calver can both also play fullback, keeping the heat on Rhyan Grant and Michael Zullo as well.
Williams, meanwhile, is expected to be at Melbourne Victory next season.
