The paper discusses the problem of speed and rotor flux magnitude estimation for the induction motor (IM) drive and presents a sliding mode observer (SMO) that is constructed based on the IM model in the synchronous reference frame. To implement the control scheme of the IM drive, generally, the speed and the flux magnitude are needed. In a control scheme with speed and flux regulation, they are used for d and q axis feedback. If the current control scheme uses a decoupling compensator, the flux and speed are needed to compute the decoupling voltages. The paper develops a SM observer for the flux magnitude based on the synchronous reference frame model of the IM. The method assumes that the d-q voltages and currents are available. The observer requires knowledge of the motor speed-instead, the SMO is fed with a speed estimate (assumed inaccurate). Using a specific gain design, the SMO is made insensitive to the input speed inaccuracy. Using the equivalent controls of the observer, the initial speed estimate is corrected to obtain two secondary speed estimates. A weighted average speed estimate that combines the secondary estimates is also shown. The theoretical findings are supported with simulations.