In one respect, mathematical fictionalists offer a uniform semantics for mathematical and scientific discourse, in another respect, they don't. Initially, both types of discourse are assessed in the same way. Electrons and relations among them make certain quantum-mechanical statements true; in turn, mathematical objects and relations among them make the corresponding mathematical statements true. It just happens that, as opposed to electrons on a realist interpretation of quantum mechanics, mathematical objects do not exist. Hence, as noted, existential mathematical statements, such as ‘there are infinitely many prime numbers’, are false. Although the resulting truth-value assignments for existential statements conflict with those found in mathematical practice, at least the same semantics is offered for mathematical and scientific languages.