The S&P 500’s 9.6% rally in three weeks is looking increasingly unsustainable to some market watchers.

Concerns about the gauge include the fact that stocks often rally on signs of softness in the US economy because that means the Federal Reserve is less likely to continue raising rates. But in the end, weaker data also is just that — weaker. In addition, some technical indicators are starting to look stretched.

Strategists tracked by Bloomberg predicted on average in mid October that the S&P 500 would end the year at 4,370, but the guage had already reached 4,514.02 by Friday’s close.

Rick Bensignor, a former Morgan Stanley strategist, suggested reducing exposure by midweek if the gauge rises to near 4,560 and completes a Setup +9, a technical indicator meant to identify potential trend reversals. Matt Maley of Miller Tabak + Co. said in a note on Saturday that while markets currently cheer the weaker economic data, ultimately fundamentals will change enough to have a negative impact on equities.

“Eventually, the stock market is going to realize that a decline in inflation does not mean that the era of ‘free money’ has returned,” Maley said. Also, the S&P 500 has become overbought according to its relative strength index, “so it could/should be due for at least some sort of a short-term pullback soon.”

That comes after Bank of America Corp.’s Michael Hartnett told investors to sell into the “epic risk rally,” citing technical and macroeconomic factors. He said investors should fade the gains in areas like distressed tech and China-exposed assets.

Investors who believe that “Santa has come early” to markets may want to consider put-option spreads through year-end on companies like Expedia Group Inc., Carnival Corp., Nvidia Corp. and Intel Corp., RBC Capital Markets derivatives strategist Amy Wu Silverman wrote in a note on Saturday.

Some strategists see reasons to be optimistic. Goldman Sachs Group Inc.’s David Kostin says investors are too concerned about the corporate earnings outlook. Morgan Stanley’s Michael Wilson has been bearish much of the year, but the bank has predicted that US assets will outperform the rest of the world next year, and that American corporate earnings will trough in the first quarter.

Still, the heady advance in recent weeks has many investors on their toes.

“At least some sort of drop does seem likely at some point soon,” Maley said. “If it does, the key support level will be at 4,400. A drop below that level would take the SPX back below its trend-line from the summer high. That, in turn, would suggest that the decline is more than just a ‘breather’ — and would raise concerns about a bigger decline.”

--With assistance from Akshay Chinchalkar.