Monday’s deadline for filing your taxes is three days late, thanks to a little-known holiday that gave workers at the IRS a day off Friday: Emancipation Day.

The holiday celebrates Abraham Lincoln’s Emancipation Act, which ended slavery in Washington, DC, on April 16, 1862.

Since it was celebrated in the district Saturday, IRS employees were given off from work the day before. That pushed the filing deadline to Monday.

Select post-office locations will remain open for last-minute filers.