In disjunctive arguments the fallacy consists of the imperfect disjunctive, either in the form of missing disjuncts or non-exclusivity (when one assumes that affirming one disjunct means that the other must be false when in fact it is possible for both to be true).

Ruggero J. Aldisert, Agatha D. Aldisert, Logic for Lawyers- A Guide …, loc. 783