Parks Canada has shut down Province House in Charlottetown for the next two months.
The closure is to allow crews to fix ceiling plaster in the building. A large of chunk of plaster recently fell from an area near the Grafton Street entrance.
Province House, built in 1847, still houses the provincial legislature. It is also a national historic site because it hosted the Charlottetown Conference in 1864, the first of a series of meetings that led to Confederation.
Workers will repair the ceiling in and around the main stairwell. Parks Canada had hoped to keep the building open to visitors, but changed its mind Thursday.
"While that work is being done there's a fair bit of dust," said Charles MacKay, clerk of the legislative assembly.
"Staff of the legislative assembly, specifically the clerk's office and the speaker's office, have temporarily relocated."
Seven employees working in the building have been moved out over concerns about air quality.