But the caveats have gone unheeded. In one example, smaller options investors, defined as those who typically trade 10 contracts or fewer in one transaction, last week purchased more than 4.5 million calls, an amount that before this January was unprecedented in records going back to 2000, data compiled by Sundial Capital Research Inc. showed.

While the rush to bet on higher share prices has helped the market stay buoyant this month amid an interest-rate increase from the Federal Reserve and growing trade tensions, it also sets up bulls for pain should things reverse in coming months.

“This is fine for now, but we think by year end such a ‘risk on’ hierarchy will be misplaced given the more uncertain outlook posed by ‘peaky’ growth rates and ever tightening financial conditions,” Mike Wilson, chief U.S. equity strategist at Morgan Stanley wrote in a note to clients Monday. He urged investors to go defensive in anticipation of a rotation out of companies whose growth is tied to economic growth and upgraded utility stocks.

Wilson isn’t alone among analysts who see trouble brewing. The rally in growth stocks brought flashbacks of the internet bubble to Citigroup strategists led by Robert Buckland, even as valuation premiums are less than half of those from almost two decades ago. A collapse would bode ill for a market whose gains have been increasingly anchored on tech giants such as Amazon.com Inc. and Facebook Inc.

“Price action of the U.S. growth/value trade looks ominously similar to late 1999,” the strategists wrote. “Watch out for a growth bubble.”

Bulls have been unfazed, emboldened — as always — by a bedrock of earnings expectations that keeps getting stronger. Estimates compiled by Bloomberg show equity analysts see S&P 500 profits rising 24 percent in 2018 then 10 percent in each of the next two years.

 Related: Are the Dominoes Are Lined Up For Another Recession?