Digital Object Identifiers (DOIs) have revolutionised the way we locate, access, cite, share and track scholarly content. Every journal article that receives a DOI becomes part of a great linked network of research. Efforts are now being made to bring the historic literature, much of which is now online, into this linked network. However, as there are no rules or guidelines around registering DOIs for out-of-copyright content, this is raising serious issues around access. Crossref’s Member Obligations state that “You must have the necessary rights for the content you register”. There is no mention of how members should proceed if there are no rights. This means that, under the current DOI system, anyone can assign a DOI to an out-of-copyright journal article, and there is nothing stopping them from putting “their” DOI’d version of that out-of-copyright article behind a paywall. The major scholarly commercial publishers have now uploaded and assigned DOIs to thousands of out-of-copyright articles, many going back as far as the 1700s. If you want to access them, you need to pay (these include articles by Charles Darwin and Alfred Russell Wallace). In many cases, open access versions of this content exist on other websites (such as on the Biodiversity Heritage Library), but anyone citing these articles must quote the DOI (as per their Crossref agreements) and thus point their readers to the versions behind paywalls. There is no doubt that bringing this historic literature into the DOI system has made it infinitely more discoverable, citable and trackable, but at what cost?