The lurches in technology stocks this week are sending a warning to environmental, social and governance-focused funds: Your former superstars may now weigh you down.

While the Nasdaq 100 Index rose for the first time in three days on Wednesday, it’s still down about 1.6% on the week. This will be felt through many ESG ETFs, since tech giants such as Apple Inc. and Microsoft Corp., with their relatively small impacts on the environment, are heavily represented in socially conscious portfolios.

For example, the largest ESG Fund, BlackRock Inc.’s $11.6 billion iShares ESG Aware MSCI USA exchange-traded fund (ticker ESGU), has a 28% stake in tech — its biggest sector. And the $5.2 billion iShares ESG Aware MSCI EM ETF (ESGE) has a 20% weighting to tech.

While that’s helped fuel gains so far this year, tech’s hefty share in ESG funds could be a headwind as investors pin their hopes on an economic reopening. This week’s potential breakthrough in Covid-19 vaccines has frayed the so-called stay-at-home trade.

“A rotation away from tech, particularly if that’s combined with the traditional energy sector coming back into favor, could spell doom for ESG ETF performance,” said Nate Geraci, president of the ETF Store. “There’s the potential for meaningful underperformance in this space that I’m not sure ESG investors are fully aware of.”

While not every ETF in the category is overweight tech, the top-performers are. The $205 million Nuveen ESG Mid-Cap Growth ETF (ticker NUMG) has a 35% allocation to tech stocks and has gained over 29% year-to-date, handily beating the S&P 500’s 9.7% showing. Nearly 30% of the $2 billion iShares MSCI USA ESG Select Social Index Fund (ticker SUSA) is in tech shares, fueling the fund’s 16% gain in 2020.

There have been 21 ESG ETFs launched so far in 2020, compared with 10 in all of 2019. Meanwhile, a record $24 billion has poured into ESG-dedicated ETFs this year, according to data compiled by Bloomberg. ESGU — whose largest holdings are Apple, Microsoft and Inc. — is responsible for half of this year’s haul, potentially boosted by issuers’ own cash.

Of course, socially-conscious investing is theoretically concerned with loftier ideals than returns alone. Still, money managers should be cognizant of whether their portfolios look particularly top-heavy, according to J O Hambro Capital Management’s Giorgio Caputo.

“For managers that are ESG aware, you don’t necessarily have to have all your eggs in the tech basket,” said Caputo, a senior fund manager. “You just want to make sure you’re on top of your risk exposure and you’re not out over your skis in one particular direction.”

This article was provided by Bloomberg News.