out of range exception (except it isn't)

[jokul]

i'm using visual studio 2010 and i'm getting the error:

Unhandled Exception: System.ArgumentOutOfRangeException: startIndex cannot be larger than length of string.

Occuring on a call to Substring(int,int);

here's my code (it's testing so there are magic numbers):

            //No out of bounds exceptions
            int temp = end - 150;
            
            if (temp > 0)
            {
                source = source.Substring(temp, end);
            }

source is approximately 32000 characters in length and end is looking at index ~18000 (and obviously temp is index less 150). I have tested it with the parameters such as:

            source = source.Substring(0,end);

and there is no problem, but i have no idea why it would not work with temp. i have tried using a dummy string variable, but as i figured it has nothing to do with the assignment source = source.Substring...

No idea how this can be the case >_>

EDIT: nevermind, i misremembered Substring (second parameter is the number of characters you want to copy).