Sorry, two-stroke penalty. It doesn't segfault under Win32:

C:\>perl -e "undef a"
Can't modify constant item in undef operator at -e line 1, at EOF
Execution of -e aborted due to compilation errors.

C:\>perl -v

This is perl, v5.6.1 built for MSWin32-x86-multi-thread
(with 1 registered patch, see perl -V for more detail)

Copyright 1987-2001, Larry Wall

Binary build 628 provided by ActiveState Tool Corp. http://www.ActiveS
+tate.com
Built 15:41:05 Jul  4 2001
[download]

I just realized your sig is longer than your golf program. ;-)

Update
Sorry Juerd, the penalty is four strokes. No segfault under 5.00502 on HP-UX either:

$ perl -e 'undef a'
Can't modify constant item in undef operator at -e line 1, at EOF
Execution of -e aborted due to compilation errors.
$ perl -v

This is perl, version 5.005_02 built for PA-RISC1.1

Copyright 1987-1998, Larry Wall
[download]

Now I'm starting to feel bad....

Update 2
Whoops! The rules did specify 5.6.1. My bad. Just two strokes off, then.