Also note that had you been using warnings, your warning message would have been more enlightening.

>perl -w -Mstrict -le
"my $n = hex '0x100000000';
 print $n;
"
Integer overflow in hexadecimal number at -e line 1.
Hexadecimal number > 0xffffffff non-portable at -e line 1.
4294967296
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