The paper straw trend has been sweeping the world following calls for increased sustainability, but as it turns out, the paper straws used by McDonald’s aren’t exactly doing the environment any favors. Last year in the UK, the fast-food chain replaced millions of single-use plastic straws with paper straws, but according to an internal memo revealed by The Sun, those paper straws can’t actually be recycled and should be “disposed of in general waste until further notice.”

Although the material used to make the paper straws is recyclable, the straw’s thickness makes it too difficult for waste solution providers to process. The reason behind the straws’ thickness is that customers complained that the original paper straws became too soggy in their drinks, Eater reported.

Contrary to the new paper ones, the plastic straws previously used by the fast-food chain were recyclable.