Expecting is different from enforcing in the contract, as is the case with interest/usury. As long as the contract allows for a gain or loss (other caveats hold

Expecting is different from enforcing in the contract, as is the case with interest/usury. As long as the contract allows for a gain or loss (other caveats holding), then it should be fine in general. On a side note, there is no strict definition of what "Islamic banking" is, much of so called Islamic banking you hear about today, isn't.