  The location of B supergiants in the Hertzsprung-Russell diagram (HRD)
represents a long-standing problem in massive star evolution. Here we propose
their nature may be revealed utilising their rotational properties, and we
highlight a steep drop in massive star rotation rates at an effective
temperature of 22000 K. We discuss two potential explanations for it. On the
one hand, the feature might be due to the end of the main sequence, which could
potentially constrain the core overshooting parameter. On the other hand, the
feature might be the result of enhanced mass loss at the predicted location of
the bi-stability jump. We term this effect "bi-stability breaking" and discuss
its potential consequences for the evolution of massive stars.
