Range attribute for the decimal value

Question

I have the following

/// <summary>The project budget</summary>                
[Range(0, double.MaxValue, ErrorMessage = "Must be a positive number")]
public double? Budget { get; set; }

But the values like "7.5" or "7,5" (culture format variant) does not pass the validation. Why?

Could the nullable double? type be the cause?

PS. Just tested, the non-nullable decimal value does not change the behavior, I have the same results..