This paper describes a project aimed at converting a legacy representation of English idioms into an XML-based format. The project is set in the context of a large electronic English-Polish dictionary which contains several hundred formalized idiom descriptions and which has been released under the terms of a free license. In short, the project consists of three phases: cleaning up the dictionary markup, extracting the legacy idiom representations, and converting them into TEI P5 XML constrained by a RelaxNG grammar created for this purpose and constituting a module that can be included as part of the TEI P5 schema. The paper contains general descriptions of the individual phases and several examples of XML-encoded idioms. It also suggests some directions for further research, which include abstracting the XML-ized idiom representations into general syntactic patterns and using the representations to automatically identify idioms in tagged corpora.