How to use std::chrono::milliseconds as a default parameter

Question

Scenario
I have a C++ function which intakes a parameter as std::chrono::milliseconds. It is basically a timeout value. And, it is a default parameter set to some value by default.

Code

#include <iostream>
#include <chrono>

void Fun(const std::chrono::milliseconds someTimeout = std::chrono::milliseconds(100)) {
    if (someTimeout > 0) {
        std::cout << "someNumberInMillis is: " << someNumberInMillis.count() << std::endl;
    }
}

int main() {
    unsigned int someValue = 500;
    Fun(std::chrono::milliseconds(someValue))
}

Issue
All of above is okay but, when I call Fun with a value then fails to compile and I get the following error:

No viable conversion from 'bool' to 'std::chrono::milliseconds' (aka 'duration >')

Question:
What am I doing wrong here? I want the caller of Fun to be explicitly aware that it is using std::chrono::milliseconds when it invokes Fun. But the compiler doesn't seem to allow using std::chrono::milliseconds as a parameter?

How use std::chrono::milliseconds as a default parameter?

Environment
Compiler used is clang on macOS High Sierra

Answer 1

With the other syntax errors fixed, this compiles without warnings in GCC 9:

#include <iostream>
#include <chrono>

void Fun(const std::chrono::milliseconds someNumberInMillis
                                         = std::chrono::milliseconds(100))
{
    if (someNumberInMillis > std::chrono::milliseconds{0}) {
        std::cout << "someNumberInMillis is: " << someNumberInMillis.count()
                  << std::endl;
    }
}

int main()
{
    unsigned int someValue = 500;
    Fun(std::chrono::milliseconds(someValue));
}