OP_REPLY in the MongoDB wire protocol includes a "startingFrom" field. It is defined as a signed 32 bit integer. That's unfortunate since a MongoDB collection can have a much larger number of documents. PyMongo currently validates this field, so a user that iterates a large collection (more than 2147483647 documents) will receive an error when the server overflows the startingFrom value and returns a negative number.

The consensus of opinion seems to be that validating this field isn't particularly useful, so PyMongo should remove the check.