The telicity behavior of degree achievements has been a puzzling problem for many linguists. The most successful and currently standard theory (Kennedy and Levin 2008) treats them as degree expressions based on different scales, which in turn influence the resulting telic or atelic interpretation. While it may account for English, this theory does not hold up cross-linguistically. We challenge the scalar theory with new Slavic data and show that verbal prefixes influence the telicity interpretation of degree achievements more than their underlying scales do. We hypothesize that the atelic/telic interpretation of the prefixed degree achievements is related to the unbounded/bounded algebraic denotation of the prefixes. In this, we follow Zwarts (2005) and his theory of the prepositional aspect. In our proposal, we formalize this contribution as an addition of two type-shifters, morphosyntactically realized as prefixes, which, as a result, have a telicizing or atelicizing effect on the given degree achievement.