ERROR: out of overflow pages in hash index

Anyone know if this can be remedied?

ERROR: out of overflow pages in hash index ....

This occurred while waiting for a hash index to be created on a 1,580
GB table (Postgres 11.7). We have > 30 TB of space free.

Here's the line where I think it gets triggered.

https://github.com/postgres/postgres/blob/7559d8ebfa11d98728e816f6b655582ce41150f3/src/backend/access/hash/hashovfl.c#L283

And I found that
#define HASH_MAX_BITMAPS Min(BLCKSZ / 8, 1024)

So there looks like a maximum size here, but I couldn't find anything
in the documentation.

What is the maximum size? I am guessing partitioning the table
someway might be a workaround, but it doesn't lend itself very well to
partitioning (i.e. there's no year column, or category or some such).

Help is appreciated!

Adam