The broom moth Ceramica pisi, a native species in Iceland, has shown a marked expansion from south Iceland towards the north, concurrent with increasing temperatures. Winter temperatures have increased more than summer temperatures in Iceland and, in the present study, the hypothesis was that the winter warming has facilitated the range shift of C. pisi. Winter survival of pupae in Iceland was studied in the laboratory. Pupae were collected in the autumn of 2012 at five separate locations, then weighed and placed at temperatures from -6 to -18 degrees C. One month after the sub-zero treatments, the pupae were placed at room temperature and pupal emergence was recorded. No significant effect of sub-zero treatments on the survival of C. pisi pupae was found. The primary hypothesis of the present study was therefore rejected. The major factor affecting low temperature survival of C. pisi pupae, however, was their autumn weight. The response was sigmoid and the 5%, 50% and 95% likelihoods for winter survival were at 157, 274 and 393 mg autumn pupal mass, respectively. This finding indicates that factors other than winter temperature, such as summer available thermal budget for larval growth, may be a limiting factor to the spread of C. pisi in Iceland.