Dust emission from the lensed Lyman break galaxy cB58

We detect 1.2 mm continuum emission from dust in the gravitationally lensed Lyman break galaxy MS1512+36-cB58. Our detected flux is surprisingly low: relative to local starburst galaxies, cB58 appears to produce somewhat less far-IR emission than its UV reddening predicts. After comparing several di fferent estimates of the source's dust content, we conclude that the appare nt discrepancy is most likely related to uncertainty in its UV spectral slo pe. Alternate scenarios to account for a far-IR "deficit" which rely on a h igh dust temperature or differential magnification are less satisfactory. O ur result underscores one of the risks inherent in characterizing the cosmi c star formation history from rest-UV data alone.