I am almost sure this question was already asked somewhere (I couldn't find it). Still why my em dash and the word proceeding it are typeset out of margins?

the source is
proliferation---nextword
Has it something to do with the hyphenation of the word proliferation?
I am using the package microtype if it matters and I tried what suggested in this answer (although the problem is slightly different).
microtypepackage. – Peter Grill Mar 05 '14 at 04:54\Dashwhile I am not using any command but---. Any way around? – Francesco Mar 05 '14 at 05:21