Distinct doesn't work with aggregator feed title

I am using the core aggregator module to pull in maybe 100 different feeds. When I make a view selecting the field "Aggregator feed: Title", the feed title is listed once for every item in the aggregator database. I only want each title listed once in the view. To fix this, I tried the "distinct" option, but nothing changes either in the live preview or page view.

Thanks for any help with a fix or workaround.