Officials in Beijing have ruled that public restrooms in the Chinese capital can have no more than two flies in them at one time, the BBC reports.

New rules issued Monday by the Beijing Municipal Commission of City Administration and Environment also regulate ads within the bathrooms and state that no more than two pieces of trash can be left uncollected for more than a half-hour.

The rules apply to bathrooms in tourist spots such as parks, railway stations, supermarkets and malls.

The "two-fly rule" was instituted as a way to clean up the toilets, which are said to be notoriously filthy. According to China Daily, the rules are not compulsory and are intended only to improve sanitation.

Copyright 2016 NPR. To see more, visit http://www.npr.org/.