ABSTRACT Cross-linguistically, spatial expressions display a propensity to undergo semantic extensions, thus frequently giving rise to grammatical markers. Drawing on diachronic material derived from the Corpus of Historical American English and synchronic data extracted from the Corpus of Contemporary American English, this study reports on a hitherto unexplored, incipient change of this kind, namely that affecting the multiword string a/one step away from. It is shown that with the conventionalization of the invited inference of closeness, the construction at issue was reanalyzed as a complex preposition, functioning initially as an exponent of prospective aspect, then additionally as a similitude marker, and finally also as an approximator. This chronology further finds reflection in the current functional gradience of a/one step away from, in that among its grammatical instances, which amount to slightly more than half the tokens in the sample, aspectual uses constitute the largest proportion, followed by similative occurrences and degree modifier attestations. At the distributional level, the investigated case of grammaticalization manifests itself in the highly confined determination and modification patterns of the form step, counterbalanced by the entire expression’s compatibility with inanimate subjects as well as host-class expansion to abstract NPs, verbal gerunds, and adjectives.