If corn is not part of your diet, I suggest swapping in an equal amount of arrowroot powder instead or double the amount of tapioca starch instead. Just be sure to use the sauce right away, as these thickeners don't hold up as well as cornstarch. Also, please note that if you use tapioca starch, you should keep the sauce to a simmer rather than boiling. Boiling tapioca thickened sauces can create unappealing stringy masses in the sauce.