require 5.6.0 is a v-string require. If it's got more then one decimal point, the "v" isn't required. (BTW, one of my favorite ways for somthing to break when you upgrade perl: In new versions of the autoconf package in debian, autoconf is a wrapper script to figure out what version of autoconf should be called. Using subs named v250 and v213, which new perls give a simple "syntax error" on. (BTW, my ++ goes to whoever can figure out exactly why this is a syntax error, and doesn't create and call ú() and Õ().)