How to use the ternary operator inside an interpolated string?

I'm confused as to why this code won't compile:

var result = $"{fieldName}{isDescending ? " desc" : string.Empty}";

If I split it up, it works fine:

var desc = isDescending ? " desc" : string.Empty;
var result = $"{fieldName}{desc}";

According to the documentation:

The structure of an interpolated string is as follows:

{ <interpolationExpression>[,<alignment>][:<formatString>] }

The problem is that the colon is used to denote formatting, like:

Console.WriteLine($"The current hour is {hours:hh}")

The solution is to wrap the conditional in parenthesis:

var result = $"Descending {(isDescending ? "yes" : "no")}";