Optical module (10; 110; 210) for a lighting and/or signalling device for a motor vehicle comprising: - a first optical deflection element, - a holder (20; 120; 220) for this optical deflection element, said first optical deflection element being attached to said holder, wherein said holder (20; 120; 220) comprises adapter fixing means (26; 126; 226) adapted to fix an adapter to which a light source is attached or to receive a fixing member thereof, - an adapter (70; 170; 270) attached to said optical deflection element holder (20; 120; 220) via said adapter fixing means (26; 126; 226), the adapter (70; 170; 270) comprising a support block; - at least one light source fixed directly or indirectly to said adapter and emitting light rays towards said first optical deflection element, said holder (20; 120; 220) being arranged to let these light rays pass, wherein said holder (20; 120; 220) comprises: - a day opposite the optical deflection element, - guide vanes (23; 123) on both sides of this day, - bearing surfaces between this day and these guide vanes (23; 123), said guide vanes (23; 123) being arranged so as to allow the adapter support block of the width close to the distance between these guide vanes to be guided to position it in contact with these bearing surfaces, characterized in that: - said first optical deflection element comprises adapter indexing means (61, 62); - said adapter (70; 170; 270) comprises complementary indexing means (71, 72) cooperating with said adapter indexing means (61, 62) so that said adapter (70; 170; 270) and the first optical deflection element are positioned relative to each other along two distinct and intersecting axes (X, Y). - a first optical deflection element, - a holder (20; 120; 220) for this optical deflection element, said first optical deflection element being attached to said holder, - an adapter (70; 170; 270) attached to said optical deflection element holder (20; 120; 220) via said adapter fixing means (26; 126; 226), the adapter (70; 170; 270) comprising a support block; - at least one light source fixed directly or indirectly to said adapter and emitting light rays towards said first optical deflection element, said holder (20; 120; 220) being arranged to let these light rays pass, wherein said holder (20; 120; 220) comprises: - a day opposite the optical deflection element, - guide vanes (23; 123) on both sides of this day, - bearing surfaces between this day and these guide vanes (23; 123), said guide vanes (23; 123) being arranged so as to allow the adapter support block of the width close to the distance between these guide vanes to be guided to position it in contact with these bearing surfaces, - a day opposite the optical deflection element, - guide vanes (23; 123) on both sides of this day, - bearing surfaces between this day and these guide vanes (23; 123), said guide vanes (23; 123) being arranged so as to allow the adapter support block of the width close to the distance between these guide vanes to be guided to position it in contact with these bearing surfaces, - said first optical deflection element comprises adapter indexing means (61, 62); - said adapter (70; 170; 270) comprises complementary indexing means (71, 72) cooperating with said adapter indexing means (61, 62) so that said adapter (70; 170; 270) and the first optical deflection element are positioned relative to each other along two distinct and intersecting axes (X, Y).