Recent ERP studies have uncovered a phenomenon we will call the "semantic illusion" effect: Words that make a sentence semantically anomalous do not cause an increase in N400 amplitude, as if the implausible sentence is temporarily taken as plausible. For instance, in "The javelin has the athletes thrown" (literal translation from Dutch) the thematic role assignment prescribed by the syntax -- "javelin" is AGENT (who does the throwing) and "athletes" are PATIENT (who are thrown) -- seems to be temporarily overcome by the preferred role assignment of the entities involved. Instead of an N400, a P600 is seen. Hoeks et al. (submitted) suggested that the effect might disappear if the processor were given more time to resolve the thematic processing difficulty. To test this hypothesis, we conducted an experiment in which sentence length was manipulated by inserting three-word prepositional phrases (e.g., "in the morning") before the final word, to permit timely construction of the correct semantic representation. The results show, however, that this manipulation did not prevent the semantic illusion effect from occurring: The implausible sentence caused little or no N400 effect as compared to a plausible control and the P600 was still apparent. Thus, the semantic illusion effect seems rather robust, as the thematic processing difficulty may be too great to be resolved in a relatively short time. The length manipulation did produce additional significant main effects in both the N400 and the P600 time-windows, the implications of which will be discussed.