Well, you can't accuse her of not being thorough.
The Associated Press reports that a cleaning woman at the Ostwall museum in Dortmund, Germany who thought she was scrubbing away dirt was actually "cleaning" part of a $1.1 million piece of art.
"When it Starts Dripping from the Ceiling," a sculpture by Martin Kippenberger, features a lattice of pieces of wood above a container that the artist painted to look like it contained a puddle of dirty water.
A cleaning woman who thought that the painted puddle of water was actually a stain scrubbed it until it was clean, AFP reports.
"It s now impossible to return it to its original state," a museum spokeswoman said, according to The Telegraph.
The work by Kippenberger, a German-born artist who died in 1997, was on loan to the museum from a private collector, who agreed that it should remain on display despite the incident, said Dortmund city spokeswoman Dagmar Papajewski. In the meantime, insurance adjusters are assessing the damage.
It has not yet been decided whether the patina would be restored, or if the artwork would be left in its newly "cleaned" condition, Papajewski said.
According to the BBC, the cleaning staff had been instructed to stay 20cm (about 8 inches) away from the artwork.
Kippenberger isn't the first artist to have his work "cleaned up." AFP reports that a work of art by Joseph Beuys was mopped clean at Düsseldorf's Academy of Fine Arts in 1986.
LOOK: "When it Starts Dripping from the Ceiling," by Martin Kippenberger: