List Intersect returning null

I have two List<FileInfo> and I want to return the common FileItem between them.

List<FileInfo> outputList = new List<FileInfo>();
outputList = list1.Intersect(list2).ToList();

However, I'm getting back an empty List.

Both the lists contain FileInfo's found by

System.IO.DirectoryInfo dir = new System.IO.DirectoryInfo(startFolder);
IEnumerable<System.IO.FileInfo> fileList = 
dir.GetFiles("*.*", System.IO.SearchOption.AllDirectories);

And filtered by queries.