Path.Combine w/ UNC Root

I am trying to combine two paths using System.IO.Path.Combine(str1, str2) but it's not working. Here is my code:

Dim str1 as string = "\\server1\share"

Dim str2 as string = "filenotfound.jpg"

Dim path as string = System.IO.Path.Combine(str1, str2)

Path is always equal to str2. For some reason Path.Combine() doesn't work with UNC filenames. Is there a built-in function that can combine a filename with a UNC root?