In French, the syllable is an early and robust prelexical and segmental unit during reading acquisition. However, most of the research dedicated to the role of the syllables in silent reading focused on its statistical and distributional properties to account for the syllable effects. But is syllable segmentation possible when no reliable statistical and distributional information is available? We proposed that the sonority – a universal phonological element – might be another source for syllable segmentation even in children with a phonological deficit. We therefore studied whether dyslexic children (DY) compared with chronological age-matched (CA) and reading level-matched controls (RL) are sensitive to universal sonority-related markedness within the syllable boundary. Forty-five French-speaking children participated. We used an adapted version of the illusory conjunction paradigm with disyllabic pseudowords (the black-colored target-letter preceded the bicolored pseudoword). The statistical and distributional properties were null or quasi-null around and within the syllable boundary, while sonority-related markedness was manipulated along a continuum from legal, unmarked clusters (e.g., lv) to illegal, marked ones (e.g., jr). Our results show that syllable segmentation strategies depend on sonority-related markedness. As markedness decreases, children better detect the syllable boundaries (lv > jr), while as markedness increases, children promote syllable onsets (jr > lv). This is true with DY children and controls. These results suggest that 1) sonority (co-)contributes to the syllable segmentation; 2) DY children have intact sensitivity to universal phonological restrictions on syllable boundaries; however, DY children are slower than controls. While this universal phonological sensitivity does not depend on reading level, syllable segmentation develops with reading experience (CA = DY > RL).