Although social media appear to be welcoming spaces that enable easy access to target-language communities, second language (L2) participation is not necessarily full and equitable. Drawing on computer-mediated discourse analysis (Herring, 2007) and critical discourse analysis (Wodak & Meyer, 2009), this analysis of a discussion forum on the social media platform Reddit uses social positioning theory (Harré, 2012; see also Debray & Spencer-Oatey, 2019) to show how L2 errors are construed as obstacles to full participation. I argue that linguistic gatekeeping is linked to community norms that reproduce language ideologies, affirm the authority of the idealized native speaker, and position L2 participants as L2 learners rather than L2 users. When L2 users cannot participate fully in what seem to be welcoming spaces they may exclude themselves. At the same time, the data also provide compelling evidence that Reddit offers a new mode of inclusion for L2 users.