Two major mechanisms of encoding telicity across languages are either marking the object as exhaustively countable or measurable, or utilizing a specific prefix on the verbal form. English predominantly uses the first mechanism, while Russian mostly utilizes the second. The learning task of an English speaker acquiring Russian, then, is two-fold: to learn each individual verb with its subset of perfective prefixes, and to acquire knowledge of the fact that most prefixed verbs denote telic events. Sixty-six English-speaking learners of Russian as well as 45 controls took an on-line test of semantic interpretation. Results indicate that some low intermediate learners, and the majority of high intermediate and advanced learners are highly accurate in interpreting Russian telicity marking. It is argued that the difficulty in acquiring Russian aspect lies in learning the lexical items signaling telicity, but crucially "not" in learning the grammatical mechanism for telicity marking. [Funding for this research was provided by the Center for Russian, East European, and Eurasian Studies of the University of Iowa International Programs.]