A method of starting a turboshaft engine (5) of an aircraft (1), said aircraft (1) being provided with a rotary wing, said aircraft (1) having a freewheel (15) interposed in a drive train (10) between said engine (5) and a rotor (2) of said rotary wing (1), said engine (5) comprising a gas generator (6) and a free turbine (9), the drive train (10) including an upstream portion (11) connecting said free turbine (9) to said freewheel (15), the method comprising the following steps: measuring the torque (Tq) exerted on said upstream portion (11), and measuring a speed of rotation (Ng) of said gas generator (6); comparing said torque (Tq) with a torque threshold (Stq) and comparing said speed of rotation (Ng) with a gas generator speed threshold (Sng); and stopping said engine (5) when said torque (Tq) is less than the torque threshold (Stq) and when said speed of rotation (Ng) is greater than the gas generator speed threshold (Sng).