We investigate how supervision (in the form of explicit instruction) interacts with distributional learning in the acquisition of the perception of a novel vowel contrast in a second language. An experiment with non-Dutch-speaking Bulgarians reveals that listeners who receive bimodal distributional training without explicit instruction can acquire new Dutch vowel contrasts, and that listeners who receive the same training with explicit instruction do not acquire the new contrasts nearly as well. We conclude that explicit instruction hampers distributional learning.