Get all properties on a class that are a specific open generic type

If I have the following generic class:

public class Gen<T>
{
    public T Value { get; set; }
}

And a class that uses it:

public class Thing
{
    public Gen<int> GenIntProperty { get; set; }
    public Gen<string> GenStringProperty { get; set; }
    public string NoGenericProp { get; set; }
}

Using reflection, how can I get just the properties that are based on the open generic type Gen<T>, specifically GenIntProperty and GenStringProperty?

I've tried various forms of this code, but I keep running in to errors like this due to not being able to reference the open generic type.

Using the generic type 'UserQuery.Gen' requires 1 type arguments

var genProps = typeof(Thing).GetProperties(BindingFlags.Public | BindingFlags.Instance)
.Where(pi => pi.PropertyType == typeof(Gen));