The rector of Notre Dame Cathedral says the Paris landmark is still so fragile that there’s a “50% chance” the structure might not be entirely saved, because scaffolding installed before this year’s fire is threatening the vaults of the Gothic monument.

Monsignor Patrick Chauvet said restoration work isn’t likely to begin until 2021 — and described his “heartache” at not being able to celebrate Christmas services inside Notre Dame this year, for the first time since the French Revolution.

“Today it is not out of danger,” he told The Associated Press on the sidelines of Christmas Eve midnight Mass in a nearby church. “It will be out of danger when we take out the remaining scaffolding.”