A mount structure for mounting an ancillary engine unit to a gas turbine engine is provided. The mount structure has plural elongate struts which each extend from a connector portion at one end of the strut to a fastening portion at the other end of the strut. The housing of the ancillary engine unit is formed of a first material having a first coefficient of thermal expansion, and the elongate struts are formed of a second material having a second coefficient of thermal expansion. Each elongate strut extends away from its connector portion in a direction which is crosswise to the direction of the hypothetical differential thermal strain at that connector portion. The mount structure further has a containment bracket which is configured to contain each connector portion.