I like the others' suggestions of Perl::Critic (which at least warns that "Subroutine "foo" does not end with "return"") and no indirect, the former of which I use for my modules. I just wanted to add another point that hasn't been mentioned yet: having a test suite with good code coverage (Devel::Cover) helps too; almost all of my CPAN modules have 100% code coverage. Though that's not a guarantee that everything is caught, it at least checks that each line of code is executed at least once, which would hopefully have helped in this particular situation.