How to change Django model field from Integer to Decimal field for Postgres DB?

Question

I'm trying to change the data type of a Django model field from PositiveBigIntegerField() into DecimalField().

From:

quantity=models.PositiveBigIntegerField()

To:

quantity=models.DecimalField(max_digits=8, decimal_places=2)

But when I migrate the change, it shows the following Postgres DB error:

Numeric field overflow Detail: A field with precision 8, scale 2 must round to an absolute value less than 10^6.

is there any idea how can I fix this issue?