Did you end your required file with a non-zero value? According to perldoc -f require:

The file must return true
as the last statement to indicate successful
execution of any initialization code, so it's
customary to end such a file with "1;" unless you're
sure it'll return true otherwise.  But it's better
just to put the "1;", in case you add more
statements.
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I whipped up a couple of files to test, and had no problem. try.pl looked like this:

use strict;
use warnings;

require 'try.req';

my $def = $::DEF{'two'};

mkDec($def);
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and try.req looked like this:

print "I'm loaded\n";
%DEF = (one => 1, two => 2);
sub mkDec{
  print "MkDec received ($_[0]) OK\n";
}
1;
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Output from running try.pl was

Name "main::DEF" used only once: possible typo at try.pl line 7
I'm loaded
MkDec received (2) OK
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