Comment 7 for bug 404470

Response from Sylvain Le Gall and Mehdi Dogguy:
"""
The (>> 0.3.2-2) is for transition and binNMU. The available version in
debian is 0.3.2-2+b1.

$ dpkg --compare-versions 0.3.2-2+b1 ">>" 0.3.2-2 && echo OK
OK

You can downgrade the build-depends to ">= 0.3.2" for ubuntu if you
like.
"""

http://lists.debian.org/debian-ocaml-maint/2009/07/msg00255.html
http://lists.debian.org/debian-ocaml-maint/2009/07/msg00256.html

Downgrade the build-depends to ">= 0.3.2" seems the easiest fix.