Perl 5.10+ defined-or operator (//) breaks syntax highlighting

my $confpath = $ENV{CONFIG_PATH} // './lib';
my $confile = $confpath . '/myconf.conf';

which however breaks syntax highlighting, so the second line (and any following) don't get coloured as they do by using the true-or ( || ) operator.

By the way, the defined-or-assign ( //=) operator doesn't break syntax highlighting.