A German flag - instead of Belgium's national colors - was accidentally affixed to a tree planted in 1977 by Queen Fabiola, during the last Belgian royal visit to Canada.
The tree is near a spot where visiting Belgium's King Philippe and his wife Mathilde are set to plant a sapling.
"While we were preparing for the tree planting ceremony on the grounds of Rideau Hall, it was brought to our attention that there was a mixup with a small flag that was used to help identify the tree planted by Her Majesty Queen Fabiola in 1977," Governor General Julie Payette's spokeswoman said.
"We rectified the situation immediately, prior to their majesties' arrival at the tree planting."
The governor general represents Queen Elizabeth II, Canada's head of state.
The Belgian royal couple will visit Ottawa, Toronto and Montreal in the course of their state visit.