Global index provider MSCI said on Tuesday it will temporarily cap the weight of any single issuer in its MSCI USA Enhanced Value Index at 25 per cent to address potential concentration risks.The exceptional issuer cap, to be reviewed monthly, will take effect from September 1.The move comes as a rally in a handful of US mega-cap stocks has increased concentration in equity indices, raising concerns over investors’ exposure to a small number of companies.MSCI’s stock market indices serve as benchmarks for trillions of dollars in assets held by investment funds, pension plans and asset managers to measure performance and guide investment decisions.Under the rule, if the combined weight of securities from a single issuer exceeds 25 per cent on a given day, MSCI will reduce that issuer’s weight to 20 per cent and redistribute the excess weight proportionately among the remaining issuers in the index.MSCI said it is reviewing concentration levels across its Enhanced Value indices and will soon launch a public consultation with methodology enhancement proposals to address the issue.Published on July 22, 2026