A process for the manufacture of gamma-delta-unsaturated ketones of formula (R1)(R2)C═CH—CH2—CH2—CO—R3 (I), wherein R1 is methyl or ethyl; R2 is a saturated or unsaturated linear or cyclic hydrocarbon residue and R3 is methyl or ethyl, by reacting a tertiary vinyl carbinol of formula (R1)(R2)C(OH)—CH═CH2 (II) with an isopropenyl methyl or ethyl ether of formula H3C—C(OR3)═CH2 (III) in the pre-sence of an ammonium salt as catalyst.