Jun. 29, 2017
Retail \| Fidelity Flex Small Cap Index Fund
Supplement to the Fidelity Flex℠ Funds Fidelity Flex℠ Mid Cap Index Fund Fidelity Flex℠ Small Cap Index Fund June 29, 2017 Prospectus The following information replaces footnote b to the “Annual Operating Expenses” table found in the “Fund Summary” section for Fidelity Flex℠ Mid Cap Index Fund. ^bThe fund is available only to certain fee-based accounts offered by Fidelity. Managed account clients, retirement plans, plan sponsors and/or plan participants pay a wrap fee that covers investment advisory and administrative services. The following information replaces footnote b to the “Annual Operating Expenses” table found in the “Fund Summary” section for Fidelity Flex℠ Small Cap Index Fund. ^bThe fund is available only to certain fee-based accounts offered by Fidelity. Managed account clients, retirement plans, plan sponsors and/or plan participants pay a wrap fee that covers investment advisory and administrative services.

Jun. 29, 2017

Retail | Fidelity Flex Small Cap Index Fund

Supplement to the
Fidelity Flex℠ Funds
Fidelity Flex℠ Mid Cap Index Fund
Fidelity Flex℠ Small Cap Index Fund
June 29, 2017
Prospectus

The following information replaces footnote b to the “Annual Operating Expenses” table found in the “Fund Summary” section for Fidelity Flex℠ Mid Cap Index Fund.

^bThe fund is available only to certain fee-based accounts offered by Fidelity. Managed account clients, retirement plans, plan sponsors and/or plan participants pay a wrap fee that covers investment advisory and administrative services.

The following information replaces footnote b to the “Annual Operating Expenses” table found in the “Fund Summary” section for Fidelity Flex℠ Small Cap Index Fund.

^bThe fund is available only to certain fee-based accounts offered by Fidelity. Managed account clients, retirement plans, plan sponsors and/or plan participants pay a wrap fee that covers investment advisory and administrative services.