Although European Union legal frameworks tend to conceive of sex and gender in binary terms, a growing number of countries in Europe and around the world have been increasingly allowing for third gender markers and non-binary possibilities in identity documents, passports, and public registries, of which the X marker in the sex or gender field has become the most common. However, initiatives like the X, which may initially signal trans-friendliness, must be considered alongside heightened border surveillance. As more and more European countries begin to follow this trend of expanding possibilities for registering (non-binary) gender (e.g. Malta, Denmark, Germany, the Netherlands), we look here to some illustrative examples (e.g. Nepal, Canada, Pakistan) that have been at the forefront of non-binary legal recognition to interrogate the complications and conundrums that these developments may provoke in European contexts.