The invention relates to a fastening assembly (1) for mounting a fuel rail in an engine. The fastening assembly comprises: a bracket (4) including a longitudinal axis (L) and coupled to the fuel rail, a retainer (3) comprising a first through opening (6) for receiving a bolt (2), and the bolt (2) inserted through the first through opening (6). The bracket (4) comprises a second through opening (7) for receiving the retainer (3) and the bolt (2). The retainer (3) is arranged in the second through opening (7) such that the retainer can rotate relative to the bracket (4). The cross-section of the first through opening (6) perpendicular to the longitudinal axis (L) has an elongated shape.