Traditionally, when companies needed assistance regarding internal controls, they turned to an external auditor (EA). However, now, due to an ongoing tightening of legal requirements and practices regarding the independence of EAs, this assistance has been restricted. As an alternative, companies are increasingly requesting internal audits to deliver this support. Even though internal audit function (IAF) are an important player in internal control, however, there is little academic knowledge about their impact. Based on a single‐case study in a large financial institution, this paper explores to what extent and how IAF affect internal controls. Furthermore, it assesses whether IAF add value to the company. The results suggest that the management letter process, including a step‐by‐step settlement of interactions, leads to a joint problem solving, an acceptance of all IAF's recommendations and a value‐adding outcome improving the level of internal controls.