The S&P 500 keeps printing record highs, yet Bank of America chief investment strategist Michael Hartnett has warned investors that a pattern last seen in March 2000, before the dot-com bubble burst, is unfolding right now.

The pattern is breadth.

Something went wrong.

Just 21 stocks — about 4% of the index — are currently making new highs. At the dot-com top in March 2000, the number was 20, Hartnett revealed in his latest Flow Show note published Friday.

The comparison is striking.