To assign lexical stress when reading, the Greek reader can potentially rely on lexical information (knowledge of the word), visual–orthographic information (processing of the written diacritic), or a default metrical strategy (penultimate stress pattern). Previous studies with secondary education children have shown strong lexical effects on stress assignment and have provided evidence for a default pattern. Here we report two experiments with adult readers, in which we disentangle and quantify the effects of these three potential sources using nonword materials. Stimuli either resembled or did not resemble real words, to manipulate availability of lexical information; and they were presented with or without a diacritic, in a word-congruent or word-incongruent position, to contrast the relative importance of the three sources. Dual-task conditions, in which cognitive load during nonword reading was increased with phonological retention carrying a metrical pattern different from the default, did not support the hypothesis that the default arises from cumulative lexical activation in working memory.