Please refer to Pages 2 and 3 of the Form 8962 instructions at the following link:
<a rel="nofollow" target="_blank" href="
https://www.irs.gov/pub/irs-pdf/i8962.pdf">https://www.irs.gov/pub/irs-pdf/i8962.pdf</a>
Under the section for calculating Modified AGI for Form 8662 purposes, a number of things are listed as being additive to it, that are otherwise excluded from regular income taxation. These items include foreign earned income and non-taxable social security benefits. While that reference may specifically apply to standard US social security benefits excluded from taxation as a function of US law, it's an easy conclusion to reach (and logical) that the legal intent of this definition would be to also include foreign social security benefits excluded from taxation by treaty, but similarly received by a US taxpayer.
At least that is how the IRS would almost certainly view it.
Thanks.
