(28)The calculation of the capital requirement for the spread risk sub-module with the standard formula should not impede insurance or reinsurance undertakings from investing in high-quality private placements, which are often unrated. An insurance or reinsurance undertaking may have concluded an agreement with a credit institution or investment firm to co-invest in bonds and loans for which a credit assessment by a nominated ECAI is not available. In that case, the insurance or reinsurance undertaking should be allowed to use the results of the approved internal ratings based approach of that credit institution or investment firm to calculate the Solvency Capital Requirement, provided that that credit institution or investment firm has its head office in the European Economic Area. The same should apply where an insurance or reinsurance undertaking has concluded an agreement with another insurance or reinsurance undertaking that uses an approved internal model in accordance with Article 100 of Directive 2009/138/EC.