Fix build on -CURRENT by pulling [1] in
[1] http://www.cs.unipr.it/git/gitweb.cgi?p=ppl%2Fppl.git;a=commitdiff_plain;h=c39f6a07b51f89e365b05ba4147aa2aa448febd7;hp=3a5e1e20a94cffb830182f22132b153d6691b7c5
Submitted by: Dmitrii Pasechnik <dimpase@gmail.com>