Why is checked arithmetic in .NET sometimes faster than unckecked?

CheckedArithmetic

// Code for http://stackoverflow.com/q/23736786/145173

using System;
using System.Diagnostics;

class Program
{
	static void Main(string[] args)
	{
		var s = new Stopwatch();
		s.Start();
		int a = 0;
		for (int i = 0; i < 100000000; i += 3) {
			if (i == 1000)
				i *= 2;
			if (i % 35 == 0)
				++a;
		}
		s.Stop();
		Console.WriteLine(s.ElapsedMilliseconds);
		Console.WriteLine(a);
	}
}