26 CFR §1.465-20

1. (a)General rule. The following amounts are treated in the same manner as borrowed amounts for which the taxpayer has no personal liability and for which no security is pledged—
   1. (1)Amounts that do not increase the taxpayer's amount at risk because they are borrowed from a person who has an interest in the activity other than that of a creditor or from a person who is related to a person (other than the taxpayer) who has an interest in the activity other than that of a creditor; and
   2. (2)Amounts (whether or not borrowed) that are protected against loss.
2. (b)Interest other than that of a creditor; cross reference. See § 1.465-8 for additional rules relating to amounts borrowed from a person who has an interest in the activity other than that of a creditor or is related to a person (other than the taxpayer) who has an interest in the activity other than that of a creditor.
3. (c)Amounts protected against loss; cross reference. See § 1.465-6 for rules relating to amounts protected against loss.
4. (d)Effective date. This section applies to amounts borrowed after May 3, 2004.