A method for adapting an engine to an octane number of fuel by decrementing an initial octane number. Starting with a reference setting of the spark advance in an engine operating range for a given octane number, the engine operating range being divided into a plurality of zones, each including an anti-pinking corrective value of the spark advance of the reference setting, the engine is switched to a reference setting that corresponds to a lower octane number: when a threshold value of the advance correction loop is exceeded in at least one zone, or when a counter of the number of zones, in which another threshold value of the advance correction loop is exceeded, exceeds a multi-zone threshold.