The conventional JET ICRH antenna matching system cannot respond to large and rapid load variations induced by the ELMs. Unacceptably large bursts of reflected power occur at the generators, severely limiting the ability to deliver RF power to ELMy plasmas. A wideband matching system based on prematching sliding impedances and fast frequency control is under commissioning on one of the antenna arrays. When suitably configured, the new system, which operates in 4 frequency bands inside the JET plant range, should strongly reduce the ELM-induced power reflection by rapid adjustments of generator frequency. The paper reports recent progress achieved in its commissioning. Successful operation of the fast frequency control loop has been demonstrated during ELMs, and work is underway to bring the system to full operation.