You have strict activated when using 5.12.

Write my $alpha = ...

Perl can't tell if it's a private (my) or global package (our) variable.

So it takes a guess and asks you to make it clear by prepending a name space.

our $var is basically an alias of the fully qualified $Pkg::var with the current package at declaration time.

And yes this error message is confusing because nowadays most declarations are done with my , which doesn't have a name space.