The laminar flow around a square block mounted at a short distance form the leading edge of a flat plate is investigated both experimentally and numerically. The Reynolds number, based on the obstacle width, is 1000. A detailed analysis of the junction flow shows how pressure and velocity can be influenced by the proximity between the obstacle and the leading edge of the plate. Calculations with the obstacle in the vicinity of the inlet boundary are in poor agreement with experiments. A change in the computational domain geometry in the upstream side of the plate is introduced and leads to a significant improvement of the description of the vortical structure formed upstream of the obstacle. The slight discrepancies remaining between calculations and experiments have little influence on the dynamics of the wake flow description and particularly on the frequency of vortex shedding. To cite this article: S. Rouvreau et al., C. R. Mecanique 333 (2005).