Header plate for a heat exchanger, comprising a wall (3) provided with orifices (7), and through which tubes (1) arranged in rows in a longitudinal direction (L) are intended to pass, characterized in that: said wall has (3), in cross section, a profile made up of a central portion (13) and of two lateral portions (15), the lateral portions (15) overall follow a first curve with a first radius of curvature (R1), the central portion (13) overall follows a second curve with a second radius of curvature (R2), smaller than the first radius of curvature (R1).