--- /usr/bin/pt-online-schema-change	2015-11-06 19:56:24.000000000 +0000
+++ pt-online-schema-change	2016-02-04 15:50:04.302333163 +0000
@@ -10405,6 +10405,9 @@
          push @rebuilt_constraints, $sql;
       }

+      my $tt = "SET FOREIGN_KEY_CHECKS=OFF \n";
+      $cxn->dbh()->do($tt);
+
       my $sql = "ALTER TABLE $child_tbl->{name} "
               . join(', ', @rebuilt_constraints);
       print $sql, "\n" if $o->get('print');