Methanol-to-gasoline conversion may be performed using a heavy gasoline treatment, followed by a separation operation. Methanol may be converted into a first product mixture comprising dimethyl ether (DME) under DME formation conditions. In a methanol-to-gasoline (MTG) reactor, the first product mixture may be converted under MTG conversion conditions to produce a second product mixture comprising light gasoline hydrocarbons and untreated heavy gasoline hydrocarbons. The untreated heavy gasoline hydrocarbons may be separated from the light gasoline hydrocarbons and transferred to a heavy gasoline treatment (HGT) reactor. The untreated heavy gasoline hydrocarbons may be catalytically reacted in the HGT reactor to form a third product mixture. A heavy hydrocarbon fraction may be separated from the third product mixture. The heavy hydrocarbon fraction includes heavy gasoline hydrocarbons having a lower boiling endpoint than does the untreated heavy gasoline hydrocarbons.