Warning letters may be issued to probation service users in the community on licence as an alternative action to recalling them to prison, when the risk of serious harm can be managed safely. Template-based, formalized warning letters may inadvertently increase or compound risk when working with high-risk clients with personality difficulties. As an alternative, psychologically-informed warning letters can be used. The aim of the letters is to facilitate joint meaning-making of violations and breaches of licence conditions between a client and an offender manager, whilst reinforcing boundaries in a thoughtful, empathic way. Practical guidelines are provided for writing and issuing psychologically-informed warning letters in probation when working with high-risk clients with personality difficulties, along with a case study. Finally, possible barriers to using these letters are identified and potential ways to overcome them are suggested.