Infrastructure investments, both public and private, are essential to the competitiveness of any economy. Currently, Brazil has several limitations in policies that are applied to the infrastructure sector, which directly contribute to make Brazilian products and services more expensive. One of these limitations arises from the financing requirements of projects of this nature. Obtaining part of the financing requirements in foreign currency would be an alternative for many investors; however, it would bring them the foreign exchange rate risk. This paper analyzes a proposal for a foreign exchange hedging mechanism to be offered in public-private partnerships scope, which provides investors with an option to hedge against the real foreign exchange fluctuation. The mechanism is perceived as a guarantee with has option-like characteristics, as its value varies as a function of the foreign exchange rate. Thus, this work sought to evaluate and price these foreign exchange rate guarantees based on a real options approach. Two exchange rate models were adopted to estimate future levels: a random geometric stochastic drift-free model and the GARCH-M model. The results obtained by both models indicated that use of this guarantee is favorable to the government. However it is possible that the proposal of a foreign exchange guarantee with these features could present a greater risk to the government than to the private partner. Therefore, one way to deal with this risk would be to establish a limit on the total amount obtained through the financing and a safety margin regarding the guarantees remuneration factor.