In this part of the paper we report the results of an ERP study on the processing of two types of compound future in Polish, with infinitival and participial complements. In the study we monitored the EEG correlates of two types of temporal mismatches. Tense mismatches between the future auxiliary and the past tense modifier wczoraj (‘yesterday’) relative to the jutro (‘tomorrow’) baseline resulted in a biphasic (LAN + P600) signature. Aspect mismatches between the future auxiliary and the perfective aspect of the lexical complement (relative to the imperfective baseline) triggered a widely distributed positivity with a posterior maximum (P600). In addition, we wanted to assess whether matching tense specifications in different words of a sentence can cause grammatical illusions. To this aim, we tested whether the presence of the adverb wczoraj (‘yesterday’) (specified for [past]) could give rise to an illusion of grammaticality for perfectives as l-participles (allegedly [past] marked), but not as infinitives (not having any [past] specification). Neither behavioral nor electrophysiological results of the present study provided support for this hypothesis. Rather, the findings seem to suggest that TENSE might not belong to the features that are relevant for grammatical illusions, unlike NEGATION, COMPARATIVE, CASE, NUMBER, GENDER, which have been shown to be suspectible to grammatical illusions. We conclude with a discussion of possible underlying reasons for this negative result.