The invention is a process for upgrading the thermostability of light metal hydrides, particularly substantially non-solvated, crystalline aluminum hydrides, which may contain small amounts of magnesium values, by contacting the hydride with an aqueous solution buffered at from about pH 6 to about 8, preferably at about 7, at a maximum temperature of about 70* C., preferably about room temperature, for a period of time and separating the so-treated product from the aqueous solution. Crystalline Aluminum hydride is useful as a fuel component in rocket propellants.