Simply silencing the warning is not the solution.

print chr(200);
print chr(1000);
[download]

will continue to be different than

print chr(200) . chr(1000);
[download]

as shown here:

>perl -we"no warnings qw( utf8 ); print chr(200); print chr(1000);" | 
+perl -nE"say length;"
3

>perl -we"no warnings qw( utf8 ); print chr(200) . chr(1000);" | perl 
+-nE"say length;"
4
[download]

Update: Mistakenly used 100 instead of 200 originally.