The feature [+spread glottis] ([+s.g.]) denotes that a speech sound is produced with a wide glottal aperture with audible voiceless airflow. Icelandic is unusual in the degree to which [+spread glottis] is involved in the phonology: in /h/, pre-aspirated and post-aspirated stops, voiceless fricatives and voiceless sonorants. The ubiquitousness of the feature could potentially affect the rate and process of its acquisition. This paper investigates the development of [+s.g.] in Icelandic, both in general and in a range of contexts, in a cross-sectional study of 433 typically developing Icelandic-speaking children aged two to seven years. As a feature, [+s.g.] is acquired early in Icelandic, although specific sound classes lag behind due to other output constraints. Children reach mastery of [+s.g.] by age three except in word-initial post-aspirated stops and voiceless nasals. Findings are interpreted in light of the literature on the feature and its development.