This variant on the Dewoitine D.520 was produced to test the Hispano-Suiza 12Z89 ter engine, giving 1,200 hp. The same D.520 (no.41) used to test the Merlin engine in the D.521 was used as the prototype for this variant. The new engine was installed in mid-June 1940, but the collapse of France prevented any further work, including test flights. The speed of this aircraft was estimated at 382 mph, but given the lack of any test flights that speed is no more than theoretical. The D.524 was converted back to the D.520 in the summer of 1941.