Limits of PL/SQL FOR...LOOP variable?

In 19.16, a dev has a quick anonymous block that fails with "ORA-1426: numeric overflow". It appears that the FOR...LOOP has a limit of 2G-1. I can't see where that would be documented or there's some implicit typing going on that I'm missing. From experimentation:

DECLARE
sseq NUMBER:=2147483647;
eseq NUMBER:=2147483647;
BEGIN
FOR x IN sseq..eseq LOOP
dbms_output.put_line(TO_CHAR(x));
END LOOP;
/

This works. Bumping the end sequence up by 1 and it fails at the FOR statement with ORA-1426 and nothing is output, so at compile time. I've tried adding an explicit declaration of "x", changing them all to NUMBER(12) or PLS_INTEGER, but still get the same error. I can't find any reference to this limit at:

https://docs.oracle.com/en/database/oracle/oracle-database/19/refrn/database-limits.htm

Am I missing something (very possible) or is this an undocumented limit?

Thanks,
Rich

--
http://www.freelists.org/webpage/oracle-l