Use this form to show they have adequate means of financial support and are not likely to rely on the US government for financial support. Completing and signing Form I-864 makes you the sponsor.The household member, other than the immigrant(s) you are sponsoring, must complete and sign Form I-864A, Contract Between Sponsor and Household Member. A joint sponsor files a separate form I-864 Affidavit of Support, alongside the primary sponsor when the latter's finances are insufficient. This video will help you to fill out I-864 For Joint Sponsor. Preparing an I-864 Affidavit of Support? Follow this checklist to ensure you include all necessary documents and avoid delays in approval. A Form I-864, Affidavit of Support, is required for most family-based US immigrants to show that they have adequate means of financial support. You, the sponsor (petitioner), and the joint sponsor must complete Form I-864. See tips for completing Form I-864.