  A challenging problem related to the design of polar codes is "robustness
against channel parameter variations" as stated in Ar{\i}kan's original work.
In this paper, we describe how the problem of robust polar code design can be
viewed as a mismatch decoding problem. We propose conditions which ensure a
polar encoder/decoder designed for a mismatched B-DMC can be used to
communicate reliably. In particular, the analysis shows that the original polar
code construction method is robust over the class of binary symmetric channels.
