I've got the following code:

from decimal import Decimal
d = Decimal('10')
x = max(d, 0) * 3

Mypy types max(d, 0) as a SupportsInt, which seems correct, but then complains:

test.py:3: error: Unsupported operand types for * ("SupportsInt" and "int")

I expect to be able to perform any operation between X and SupportsX if that operation is supported between X and another X.

This is mypy 0.570 and the underlying code is Python 3.6.1. I can reproduce this issue with no flags passed.