sort in prefixQuery

[lampa24]

Hello,
I use lucene. I indexed documents with two fields. First field is name and second field is count. I use this index for autocomplete. I need find 10 names by prefix and the higest count.
I use code like this :

Sort sort = new Sort(new SortField("countfieldname", SortField.INT,true));
PrefixQuery pq = new PrefixQuery(new Term("namefieldname", "prefix"));
indexSearcher.Search(pq,null,10, sort);

But it doesn't work . I get unsorted results.