The present disclosure relates to an diesel exhaust treatment device including a main body having a central longitudinal axis that extends between first and second ends of the main body. A catalyzed substrate is positioned within an interior of the main body. A side inlet is positioned at a side of the main body for directing exhaust gas into the interior of the main body. A flow distribution element is positioned within the interior of the main body at a location between the side inlet and an upstream face of the substrate. The flow distribution element extends across a direction of exhaust flow through the main body and is mounted at a side of the main body that is opposite the side inlet.